Apparatus for arc-melting cold iron source and method threof

ABSTRACT

The present invention provides an arc-melting apparatus, which attains extremely high efficiency by preheating scraps using exhaust gas from the melting chamber. The arc-melting apparatus needs for no device to carry and supply an iron source to a melting chamber, which makes it possible to preheat the next charge. The arc-melting apparatus has a melting furnace which melts scraps, a preheating shaft connected directly to an upper part of one side of the melting furnace, an arc electrode for melting scraps in the melting furnace, a bucket for supplying scraps to the preheat shaft so as to continuously maintain scraps in the melting furnace and in the preheating shaft, a tapping portion having a tapping hole, being projected outward from the melting furnace and a tilting device for tilting the melting furnace on a side of the tapping portion. The tapping portion is arranged at an orthogonal direction to the direction of the supplied cold iron source. The preheating shaft of the melting furnace and the tapping portion have a distance between the mutual part, so that scraps do not flow out on a the tapping hole side.

FIELD OF THE TECHNOLOGY

[0001] The present invention relates to an apparatus for arc-melting acold iron source such as iron scrap and direct smelting reduction iron,etc. efficiently, and a melting method thereof.

BACKGROUND OF THE TECHNOLOGY

[0002] Japanese unexamined patent publication No. 7-180975 discloses ascrap preheating device, wherein a shaft furnace is connected to anupper part of an arc furnace, and furthermore wherein one stage, or twostages or more of fire grates are attached to the shaft furnace, whichis able to be opened or closed.

[0003] Japanese unexamined patent publication No. 7-332874 discloses amethod, wherein there is arranged a first preheating chamber of rotarydrum type which is horizontally placed, connected to an upper cover of amelting chamber of an arc-furnace; and wherein there is arranged asecond preheating chamber which is connected to the first preheatingchamber at the bottom. After a cold iron source is preheated by theexhaust gas generated from the melting chamber in the second preheatingchamber, the preheated cold iron source is pushed into the firstpreheating chamber by a pusher and the preheated cold iron source ischarged into the melting chamber via the first preheating chamber whichis rotating.

[0004] Japanese examined patent publication No. 6-46145 discloses anapparatus, wherein a shaft type preheating chamber is directly connectedto a melting chamber, and wherein a charge of cold iron source ischarged into the melting chamber. As the charge is melted, a new chargeof iron falls from the shaft type preheating chamber into the meltingchamber while the cold iron source in the shaft type preheating chamberis being preheated by an exhaust gas. This continues until all of thecold iron source which is charged into the melting chamber and the shafttype preheating chamber is melted.

[0005] By means of the method and apparatus as described above, the highpreheating effect can attain an electric power unit of 250 to 270 kWh/t.However, the above described Prior Art has the following problems.

[0006] According to JP7-180975 and JP7-332874, in order to charge thepreheated cold iron resource into the melting furnace of thearc-furnace, a device for transporting the preheated cold iron sourcesuch as a pusher or a rotary drum is necessary. For this reason, thepreheating temperature has a limitation when preheating by the exhaustgas from the melting chamber. That is to say, if a large amount ofcarbonaceous material such as coke and oxygen gas are blown into themelting chamber and the cold iron source is preheated by a large amountof the generated exhaust gas having a high temperature, the preheatedtemperature becomes high and the preheating effect is improved. However,in an apparatus, high exhaust gas temperatures causes problems such asheat deformation and fusion of the above described transporting device.Therefore, the exhaust gas temperature cannot be elevated.

[0007] On the contrary, according to JP6-46145, the shaft typepreheating chamber is directly connected to the melting furnace.Consequently, the above described device for transporting the cold ironsource is not necessary and the above described problem does not occur.However, since each time the melted iron amount corresponding to onebatch is melted, all of the cold iron source in the melting chamber ismelted, the melted iron is poured off and none of melted iron is left inthe preheating chamber. For this reason, a cold iron source for the nextbatch which is to be charged immediately thereafter cannot be preheated.Therefore, this method cannot be said to be sufficient, with respect tothe effective use of exhaust gas.

DISCLOSURE OF THE INVENTION

[0008] It is an object of the present invention to provide anarc-melting apparatus for arc-melting a cold iron source which does notrequire a device for carrying and feeding the cold iron source to thepreheating chamber. This apparatus can, also, preheat the cold ironsource to be use in the following charge, and can melt the cold ironsource with an extreme high efficiency unattainable conventional meltingapparatus whereby use exhaust gas for preheat the scrap. More concretelyspeaking, an arc-melting apparatus for arc-melting cold iron source withelectric power unit of less than 250 kWh/t can be provided. Furthermore,this apparatus provides a method for melting the cold iron sourcewithout using a large scaled apparatus, and for preventing harmfulconstituents from being generated. In order to attain theabove-mentioned object, the present invention provides the followingarc-melting apparatus for arc-melting cold iron source. That is to say,

[0009] The first invention is an arc-melting apparatus for arc-meltingcold iron source comprising:

[0010] (a) a melting chamber for melting the cold iron source;

[0011] (b) a preheating shaft, which is directly connected to an upperpart of one side of the melting furnace and into which is introduced theexhaust gas generated in the melting chamber, in order to preheat thecold iron source;

[0012] (c) an arc electrode for melting the cold iron source in themelting chamber;

[0013] (d) a cold iron source feed device for feeding the cold ironsource to the preheating shaft so that the cold iron source iscontinuously maintained in the melting chamber and the preheating shaft;

[0014] (e) a tapping portion having a tapping hole, projecting into themelting chamber; and

[0015] (f) a tilting device for tilting the melting chamber on the sideof the tapping portion to pour out the melted iron.

[0016] The second invention is an arc-melting apparatus for arc-meltingcold iron source of the first invention, wherein being projected outwardfrom the melting chamber the tapping portion having a tapping hole ispositioned in a different direction from the direction toward which thecold iron source in the preheating shaft is fed to the melting chamber.

[0017] The third invention is an arc-melting apparatus for arc-meltingcold iron source of the second invention, wherein the tapping portion isarranged at a right angle to the direction toward which the cold ironsource is fed.

[0018] The fourth invention is an arc-melting apparatus for arc-meltingcold iron source of the first invention or the second invention, whichhas a distance between the position of the preheating shaft adjacent tothe melting chamber and the position of the tapping portion adjacent tothe melting chamber, in order to make it possible to prevent the coldiron source from flowing over the tapping portion, when the meltingchamber is tilted.

[0019] The fifth invention is an arc-melting equipment for arc-meltingcold iron source of the fourth invention , wherein a distance betweenthe position of the preheating shaft of the melting chamber and theposition of the tapping position is longer than a horizontal distance ofthe base of the cold iron source resting in the melting chamber from thepreheating shaft, to the melting chamber.

[0020] The sixth invention is an arc-melting apparatus for arc-meltingcold iron source of any one of the first invention through the fifthinvention, which has a travelling device for travelling the arcelectrode following the molten iron which moves in the melting furnace

[0021] The seventh invention is an arc-melting apparatus for arc-meltingcold iron source of any one of the first invention through the sixthinvention which has further another arc electrode which is placed at thetapping portion.

[0022] The eighth invention is an arc-melting apparatus for arc-meltingcold iron source of any one of the first invention through the seventhinvention which has a device for feeding oxygen gas at the lowerposition of the preheating shaft.

[0023] The ninth invention is an arc-melting apparatus for arc-meltingcold iron source of any one of the first invention through the eighthinvention which has a fuel feed device for feeding fuel together withoxygen gas to the cold iron source at the lower position of thepreheating shaft of the melting furnace

[0024] The tenth invention is an arc-melting apparatus for arc-meltingcold iron source of any one of the first invention through the ninthinvention which has a carbonaceous material feed device for feedingcarbonaceous material to the melting furnace and an oxygen gas feeddevice for feeding oxygen gas to the melting chamber.

[0025] The eleventh invention is an arc-melting apparatus forarc-melting cold iron source of any one of the first invention throughthe tenth invention which has a device for elevating the temperature ofthe exhaust gas discharged from a post-burning chamber to apredetermined temperature or more, being equipped with the post-burningchamber which post-burns the residual of non-combusted gas generated inthe melting furnace which has passed through the preheat chamber byfeeding oxygen containing gas and with a cooling portion which cools anexhaust gas discharged from the post-burning chamber.

[0026] The twelfth invention is an arc-melting apparatus for arc-meltingcold iron source of any one of the first invention through the eleventhinvention which has an adsorbent feed device for feeding adsorbent tothe exhaust gas which has been quickly cooled at the cooling portion.

[0027] The thirteenth invention is an arc-melting apparatus forarc-melting cold iron source of any one of the first invention throughthe twelfth invention. This invention has a device for burning one partor the whole of the incombustible gas generated from the meltingchamber, by arranging single or plural steps of the gas introducingholes in a range from the surface of the bath in the melting chamber tothe upper end of the cold iron source of the upper part of thepreheating shaft and by feeding oxygen containing gas through the gasintroducing holes to charge portion of the cold iron source.

[0028] The fourteenth invention is an arc-melting equipment forarc-melting cold iron source of any one of the first invention throughthe thirteenth invention. This invention has a gas feeding device forblowing an oxygen gas or an inert gas into the molten iron in thevicinity of boundary of the cold iron source in the melting chamber andthe molten iron.

[0029] The fifteenth invention is an arc-melting method for arc-meltingcold iron source comprising the steps of:

[0030] (1) introducing an exhaust gas generated in a melting chamberinto a preheating chamber to preheat the cold iron source;

[0031] (2) melting the cold iron source by an arc electrode while thecold iron source is continuously or intermittently being fed to thepreheating shaft so that the cold iron source may be continuouslymaintained in the preheating shaft and the melting chamber;

[0032] (3) tilting the melting furnace at the time when the molten ironis accumulated;

[0033] (4) heating the molten iron for a predetermined time by an arcelectrode to elevate the temperature thereof; and

[0034] (5) tapping the molten iron in the state that the cold ironsource may be continuously maintained in the preheating shaft and themelting chamber.

[0035] The sixteenth invention is an arc-melting method for arc-meltingcold iron source of the fifteenth invention comprising the step ofseparating the molten iron and the cold iron source completely bytilting the melting chamber.

[0036] The seventeenth invention is an arc-melting method forarc-melting cold iron source of the fifteenth invention or the sixteenthinvention comprising the step of blowing oxygen or the oxygen and fuelsimultaneously onto the cold iron source at the lower position of thepreheating shaft of the melting chamber.

[0037] The eighteenth invention is an arc-melting method for arc-meltingcold iron source of any one of the fifteenth invention through theseventeenth invention comprising the step of blowing oxygen andcarbonaceous material such as coke into the melting furnace.

[0038] The nineteenth invention is an arc-melting method for arc-meltingcold iron source of any one of the fifteenth invention through theeighteenth invention wherein the cold iron source of 40% or more of onecharge remains in the melting furnace and the preheating shaft duringmelting and at the time of tapping.

[0039] The twentieth invention is an arc-melting method for arc-meltingcold iron source of any one of the seventeenth invention through thenineteenth invention, wherein the sum of the oxygen being blown into thelower part of the preheating shaft and the oxygen being blown into themelting furnace is 25 Nm³/ton or more.

[0040] The twenty-first invention is an arc-melting method forarc-melting cold iron source of any one of the fifteenth inventionthrough the twentieth invention comprising the steps of:

[0041] melting the cold iron source in the melting furnace by feedingsupplementary heat source such as arc heating and coke and oxygen to themelting furnace; feeding and post-burning oxygen containing gas toelevate an exhaust gas to a predetermined temperature or more withoutdischarging to the outside of the system the residual of thenon-combusted gas generated in the melting furnace which has passedthrough the preheat chamber; and thereafter cooling the exhaust gascontinuously and quickly.

[0042] The twenty-second invention is an arc-melting method forarc-melting cold iron source of any one of the fifteenth inventionthrough the twenty-first invention comprising the steps of:

[0043] melting the cold iron source in the melting furnace by feedingsupplementary heat source such as arc heating and coke and oxygen to themelting furnace; arranging one or plural stages of gas introducing holesin a range from bath surface in the melting furnace to upper end of thecold iron source of upper part of the preheat shaft; and feeding oxygencontaining gas from those gas introducing holes to the charge portion ofthe cold iron source to burn part or all of the non-combusted gasgenerated from the melting furnace.

[0044] The twenty-third invention is an arc-melting method forarc-melting cold iron source of the twenty-first invention or thetwenty-second invention comprising the step of feeding adsorbent to theexhaust gas which has been quickly cooled at the cooling portion.

[0045] The twenty-fourth invention is an arc-melting method forarc-melting cold iron source of any one of the twenty-first inventionthrough the twenty-third invention which is characterized in that theexhaust gas after the post-burning is 900° C. or more.

[0046] The twenty-fifth invention is an arc-melting method forarc-melting cold iron source of any one of the fifteenth inventionthrough the twentieth invention comprising the steps of:

[0047] melting the cold iron source in the melting furnace by feedingsupplementary heat source such as arc heating and coke and oxygen to themelting furnace ; arranging one or plural stages of gas introducingholes in a range from the surface of the bath in the melting furnace toupper end of the cold iron source of the upper part of the preheatshaft; feeding a predetermined amount of the oxygen containing gas fromthose gas introducing holes to the charge portion of the cold ironsource to burn the non-combusted CO gas generated from the meltingfurnace; making the exhaust gas which is generated owing to burning ofthe non-combusted CO gas by the oxygen containing gas in the vicinity ofthe outlet of the preheating shaft have a predetermined temperature ormore; and thereafter cooling the exhaust gas at the cooling portionwhich is connected to the upper part of the preheating shaft.

[0048] The twenty-sixth invention is an arc-melting method forarc-melting cold iron source of the twenty-fifth invention comprisingthe step of feeding adsorbent to the exhaust gas which has been quicklycooled at the cooling portion.

[0049] The twenty-seventh invention is an arc-melting method forarc-melting cold iron source of the twenty-fifth invention or thetwenty-sixth invention, wherein the exhaust gas in the vicinity of theoutlet of the preheating shaft is 900° C. or more.

[0050] The twenty-eighth invention is an arc-melting method forarc-melting cold iron source of any one of the twenty-second inventionthrough the twenty-seventh invention, wherein the whole blowing amountof the oxygen containing gas makes feed oxygen amount Q_(IN) which iscalculated from oxygen concentration therein and flow rate therein havethe following formula (A) with respect to oxygen amount Q (Nm³/min)which is blown in the melting furnace:

0.55Q≦0.9Q  (A)

[0051] The twenty-ninth invention is an arc-melting method forarc-melting cold iron source of any one of the fifteenth inventionthrough the twenty-eighth invention comprising the steps of:

[0052] melting the cold iron source in the melting furnace by feedingsupplementary heat source such as arc heating and coke and oxygen to themelting furnace; at the time of thereof introducing air into the meltingfurnace; and burning the non-combusted CO (Mainly CO) gas in the meltingfurnace so that 0.3≦OD≦0.7 where CO₂(CO₂+CO) is made to be OD.

[0053] The thirtieth invention is one wherein a melting method formelting the cold iron source uses the arc-melting equipment of any oneof the first invention through the seventh invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0054]FIG. 1 is a perspective view showing an arc-melting apparatus,relating to one embodiment of the present invention.

[0055]FIG. 2 is a plan view showing an arc-melting apparatus, relatingto one embodiment of the present invention.

[0056]FIG. 3 is a sectional view taken on line A-A′ of FIG. 1.

[0057]FIG. 4 is a sectional view taken on line B-B′ of FIG. 1.

[0058]FIG. 5 is a sectional view showing a state of tilting a meltingfurnace of an arc-melting apparatus, relating to one embodiment of thepresent invention.

[0059]FIG. 6 is a sectional view showing a modified example of thearc-melting apparatus, shown in FIG. 1 or FIG. 5.

[0060]FIG. 7 is a graph showing the relation of an oxygen unitrequirement and an electric power unit requirement, when an operation isperformed, using the apparatus of the present invention.

[0061]FIG. 8a shows a plan view and FIG. 8b a sectional view showing anarc-melting apparatus, having a tilting portion at the bottom of thesecond embodiment of the present invention.

[0062]FIG. 9 is a sectional view showing an arc-melting apparatus,relating to the second embodiment of the present invention.

[0063]FIG. 10 is a sectional view showing a state of tilting thearc-melting apparatus, relating to the second embodiment of the presentinvention.

[0064]FIG. 11 is a sectional view showing a modified example of anarc-melting apparatus of the present invention.

[0065]FIG. 12 is a sectional view showing an arc-melting apparatus,having an oxygen feeding device, relating to an embodiment of thepresent invention.

[0066]FIG. 13 is a plan view showing an arc-melting apparatus, having anoxygen feeding device relating to an embodiment of the presentinvention.

[0067]FIG. 14 is a sectional view showing an essential portion of anarc-melting apparatus equipped with a fuel feeding device, in additionto an oxygen feeding device relating to an embodiment of the presentinvention.

[0068]FIG. 15 is a graph showing tap-tap time depending on whether thereis oxygen feed to the lower portion of the preheating shaft, relating toan embodiment of the present invention.

[0069]FIG. 16 is a sectional view of an arc-melting apparatus, equippedwith plural stages of gas introducing holes relating to an embodiment ofthe present invention.

[0070]FIG. 17 is a plan view of an arc-melting apparatus, equipped withplural stages of gas introducing holes relating to an embodiment of thepresent invention.

[0071]FIG. 18 is a sectional view of an arc-melting apparatus, equippedwith one stage of a gas introducing hole relating to an embodiment ofthe present invention.

[0072]FIG. 19 is a partially sectional view of an arc-melting apparatus,equipped with plural stages of gas introducing holes relating to anembodiment of the present invention.

[0073]FIG. 20 is a sectional view of an arc-melting equipment equippedwith an exhaust gas treatment system and a gas introducing hole,relating to an embodiment of the present invention.

[0074]FIG. 21 is a sectional view showing an arc-melting apparatus,relating to another embodiment with respect to an arc-melting apparatus,equipped with an exhaust gas treatment system and one stage of a gasintroducing hole relating to an embodiment of the present invention.

[0075]FIG. 22 is a sectional view showing an arc-melting apparatus,relating to another embodiment with respect to an arc-melting apparatus,equipped with an exhaust gas treatment system and plurality of gasintroducing holes relating to an embodiment of the present invention.

[0076]FIG. 23 is a sectional view showing an arc-melting apparatus,relating to another embodiment with respect to an arc-melting apparatus,equipped with an exhaust gas treatment system, a gas introducing holeand a post-burning chamber relating to an embodiment of the presentinvention.

[0077]FIG. 24 is a longitudinally schematic view of an arc-meltingequipment, showing an example of an embodiment of the present invention.

[0078]FIG. 25 is a graph showing results of investing influence ofoxygen blow amount on an electric power unit requirement with respect toan embodiment of the present invention.

[0079]FIG. 26 is a longitudinally schematic view of an arc-meltingapparatus, showing another embodiment relating to an embodiment of thepresent invention.

[0080]FIG. 27 is a longitudinally schematic view of an arc-meltingequipment showing another embodiment relating to an embodiment of thepresent invention.

[0081]FIG. 28 is another graph showing results of investing influence ofoxygen blow amount on electric power unit relating to an embodiment ofthe present invention.

[0082]FIG. 29 is a graph showing results of investing influence ofmolten iron mixing ratio on an electric power unit requirement, relatingto an embodiment of the present invention.

[0083]FIG. 30 is a longitudinally schematic view of an arc-meltingequipment which shows another embodiment relating to an embodiment ofthe present invention.

[0084]FIG. 31 is a plan schematic view of the arc-melting equipmentshown in FIG. 30.

[0085]FIG. 32 is a longitudinally schematic view of an arc-meltingequipment, which shows another embodiment (a melting furnace and amelting method) relating to an embodiment of the present invention.

[0086]FIG. 33 is a longitudinally schematic view of an arc-meltingequipment showing state of tilting a melting furnace among otherembodiments relating to an embodiment of the present invention.

[0087]FIG. 34 is a longitudinally schematic view of an arc-meltingequipment, which shows another embodiment relating to an embodiment ofthe present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0088] Now the first embodiment will be described with reference to FIG.1 through FIG. 7. FIG. 1 is a perspective view showing an arc-meltingapparatus, relating to an embodiment of the present invention. FIG. 2 isa plan view of the arc-melting apparatus, relating to the embodiment ofthe present invention. FIG. 3 is a sectional view taken on line A-A′ ofFIG. 1. FIG. 4 is a sectional view taken on line B-B′ of FIG. 1. Thisarc-melting apparatus is equipped with a melting furnace 1 forarc-melting cold iron source, a preheating shaft 2 directly connected toan upper portion of one side 1 a of the melting furnace and extendingupward and a tapping portion 3 arranged in a melting chamber 1.

[0089] As shown in FIG. 3, an exhausting portion 2 a which is connectedto an exhaust gas adsorption system is placed at an upper end of thepreheating shaft 2. Iron scraps S as cold iron source are charged intothe melting furnace 1 and the preheating shaft 2. A bucket 4 forcharging scraps is placed above the preheating shaft 2 and the ironscraps S are charged from this bucket 4 into the preheating shaft 2. Inorder to prevent hanging up, carbon source, for example, coke may becharged into the preheat shaft 2. In this case, charge of the scraps Sfrom the bucket 4 is performed to feed the scraps S continuously orintermittently to the preheating shaft 2 so that the scraps S arecontinuously maintained in the melting furnace 1 and the preheatingshaft 2 during the operation. The charge of the scraps S, in this case,may be carried out according to a process standard prepared in advance,based on a results of the operational performance or a sensor which candetect the amount of the scraps S in the preheating shaft 2 beinginstalled, the charge of the scraps S through the bucket 4 may becontrolled by appropriate means for controlling, based on a signaloutputted from this sensor.

[0090] A taper of a side wall of the preheating shaft 2 rangespreferably from 2.5 to 7 degrees. If this taper is less than 2.5degrees, hanging up of the scrap in the shaft cannot be effectivelyprevented. If this taper is over 7 degrees, the charge amount of scraps3 decreases. With a decreased amount of the scraps 3, there isinsufficient residence time during preheating,and it becomes impossibleto sufficiently obtain the effect of preheating. To compensate for thisand increase residence time to the same degree that is intended to begained, the height of the preheating shaft 2 must be increased. If thisis done, the building has to be heightened. Furthermore, since asectional area of an upper part of the preheating shaft 2 becomesnarrow, the amounts of scraps which can be held therein and bepreheated, is limited.

[0091] A furnace cover 5, which is capable of opening and closing, isarranged at an upper part of the melting furnace 1 and an arc electrode6 is inserted vertically into the melting furnace, passing through thefurnace cover 5 from the top of the melting furnace 1. In addition, thefurnace bottom electrodes 11 are placed in a position where theelectrodes 11 confront the arc electrode 6 at a furnace bottom of themelting furnace 1. The scraps S are melted into molten iron 8 by an arc7 which is produced by the arc electrode 6. Slag 9 is produced on themolten iron 8 and the arc 7 is formed in this slag 9. The arc electrode6 is supported by a support member 13 and can be tilted by a tiltingmechanism 14.

[0092] Two lances 12 a, 12 b are inserted turning their top ends intothe surface of the molten iron bath, the oxygen being fed through thelance 12 a and coke as a supplementary heat source being injectedthrough the lance 12 b.

[0093] The scraps S in the preheating shaft 2 are fed in the directionof going from a preheating shaft side 1 a of the melting furnace towardthe opposite side 1 b thereof, and the tapping portion 3 is arrangedprojecting out of the melting furnace 1, so as to make a right anglewith the direction to the scraps S are fed. The melting furnace 1 can betilted on a side of the tapping portion 3 (See FIGS. 4 and 5) by atilting mechanism which is not shown in the drawings. A portion wherethe preheating shaft 2 of the melting furnace 1 is placed and a portionwhere the tapping portion 3 is placed are apart as much as distance aand the scraps S are prevented from flowing out on the side of thetapping portion 3 by a wall portion thereof when the melting furnace 1is tilted. In this case as shown in FIG. 3, the distance a is preferablylonger than a distance that the scraps S extends with an angle of reposeranging from the preheat shaft 2 to the melting furnace 1. By way ofdoing in this manner, the scraps S are completely prevented from flowingout on the side of the tapping portion 3, when the melting furnace istilted.

[0094] A tapping hole 15 is formed at a bottom portion in the vicinityof the top end of the tapping portion 3 (see FIG. 4) and a stopper 16which is movable up and down, in order to open and close the tappinghole 15 is placed. In addition, a slag door 17 is placed on the top endside of the tapping hole 3.

[0095] When the iron scraps are melted in a melting equipmentconstituted in this manner, the iron scraps S are firstly charged intothe melting furnace 1 and the preheat shaft 2 so that the iron scraps Sare continuously maintained in the melting furnace 1 and in the preheatshaft 2.

[0096] In this state, the arc 7 is formed by the arc electrode 6 to meltthe scraps S. In this case, oxygen is fed through lance 12 a to assistthe melting of the scraps. After molten iron accumulates in the furnace,coke is injected as a supplementary heat source through lance 12 b intothe slag to start slag forming operations for the new scrap beingmelted, and a top end of the electrode 6 is buried in the slag 9 so thatthe arc 7 is formed in the slag 9. The coke is a supplementary heatsource which contributes to melting of the scraps S.

[0097] An exhaust gas containing CO is generated by melting the scrapsin this manner and is discharged through the preheating shaft 2 and theexhausting portion 2 a. The heat of this exhaust gas is transferred tothe scraps S in the preheating shaft 2, whereby the scraps arepreheated. Since the scraps in the preheating shaft 2 are gradually fedinto the melting furnace 1, accompanied by melting of the scraps Swithin the melting furnace 1, the upper end position of the scraps Sgoes down. Therefore, additional scraps S are continuously orintermittently fed from the bucket 4 to the preheating shaft 2, so thatthe scraps S are continuously maintained in the melting chamber and inthe preheating shaft. In this way, at least a predetermined amount ofscraps are always maintained in the melting furnace 1 and in thepreheating shaft 2. The charging of the scraps S is controlled accordingto a process standard prepared in advance based on results ofoperational performance or a sensor which can detect amount of thescraps S in the preheat shaft 2. A signal from the sensors is then usedto control the bucket 4.

[0098] As the scraps S are being melted, a state that the scraps S asiron source and the molten iron co-exist in the melting furnace 1. Andthe temperature of the molten iron becomes low, for example, 1540˜1550°C . This is only a slight super heat compared with 1530° C. ofsolidification temperature of molten iron, which can cause suchinconvenience as a blocking of the tapping hole at the time of tappingby solidified material. For this reason according to the presentinvention, arc heat is continued by tilting the melting furnace 1 on theside of the tapping portion 3 before tapping as shown in FIG. 5. In thiscase the tapping portion 3 is arranged projecting out of the meltingfurnace 1 so as to make a right angle with the direction to which thescraps S flow in, and further a portion where the preheat shaft 2 of themelting furnace 1 is placed and a portion where the tapping portion 3 isplaced are apart as much as distance a (See FIG. 3) and the scraps S areprevented from flowing out on the side of the tapping portion 3 by awall portion thereof. Owing to this prevention, area where the molteniron having flown into the side of the tapping portion 3 contacts withthe scraps S can be made to be small. Therefore, super heat (ΔT) of themolten iron can be increased and it is possible to avoid the problemthat temperature of the molten iron which is tapped is low. By makingthe separation distance a longer than the distance of the scraps S whichextends with an angle of repose, rising from the preheat shaft 2 to themelting furnace 1, the scraps S are nearly completely prevented fromflowing into the tapping portion 3. This allows the temperature of themolten iron to be elevated all the more.

[0099] If the melting furnace 1 is tilted, the arc electrode 6 ispositioned on the broken line in FIG. 5 and arc is not effectively fed.By tilting the arc electrode 6 by the tilting mechanism 14, however, thearc electrode is positioned on the solid line in FIG. 5 and the arc canbe effectively fed to the molten iron.

[0100] Instead of moving the arc electrode 6 in this manner, as shown inFIG. 6, another arc electrode 6′ is installed and when the meltingfurnace 1 is tilted, by generating the arc from the arc electrode 6′ thearc can be effectively fed.

[0101] In the manner of the foregoing, the melting progresses. When apredetermined amount of the molten iron is accumulated in the furnace,the melting furnace 1 is tilted to make small the area where the molteniron contacts with the scraps. After the molten iron is superheated byarc heat for a certain time, while the scraps S are maintainedcontinuously in the melting furnace 1 and in the preheat shaft 2 byfurther tilting the melting furnace 1, the stopper 16 which has closedthe tapping hole 15 is moved upward to open the tapping hole 15. Andthen one charge of molten iron is tapped through the tapping hole 15into a ladle.

[0102] When the scraps are melted in this manner, since the preheatshaft 2 is not equipped with a scrap carry and supply equipment such asa pusher or a finger, the preheat shaft 2 can have the oxygen amountincreased to a greater extent than in conventional melting equipmentequipped with these facilities whereby the temperature of the exhaustgas can be elevated. The melting equipment of the present invention can,therefore, preheat the scraps to higher temperature than is preheated inconventional melting equipment.

[0103] In case that the scraps S are fed to the preheat shaft 2 so thatthe scraps S are continuously maintained in the melting furnace 1 andthe preheat shaft 2 and when one charge or more of molten iron areproduced in the melting furnace to also tap the molten iron, the scrapsare continuously maintained in the melting furnace 1 and the preheatshaft 2 and for this reason, efficiency of preheating the scraps byexhaust gas is high. In this case, by realizing that the scraps of 40%or more of one charge are maintained in the melting furnace 1 and in thepreheat shaft 2, the efficiency of preheating becomes extremely high.

[0104] In addition, from a view point of melting scraps efficientlysupplementary heat source such as coke is preferably used, by feedingoxygen through the lance 12 a (FIG. 3) as well as injecting coke assupplementary heat source through the above described lance 12 b CO gasis generated in the melting furnace 1 and heat can be produced. In thiscase feed amount of oxygen is preferably 25 Nm³/t or more. Thanks tothis scraps can be melted more efficiently. The feed amount of oxygen ismore preferably 40 Nm³/t or more. FIG. 7 shows electric power unitconsumption in a melting furnace of an embodiment described later whenoxygen unit consumption is 15˜45 Nm³/t. As accompanied by increase ofthe oxygen unit consumption, the electric power unit consumptiondecreases as shown in FIG. 7, and if the oxygen unit consumption is inparticular 25 Nm³/t or more, the electric unit consumption is soextremely low as to be 200 KWh or less. Furthermore if the oxygen unitconsumption is 40 Nm³/t or more, the electric unit consumption is about120 KWh or less, which is a furthermore low value.

[0105] Since as described above, according to the above describedembodiment facilities such as a pusher or a plunger are not necessary,temperature of the exhaust gas can be elevated and since the scraps Scan continuously be maintained in the melting furnace 1 and in thepreheating shaft 2, the efficiency of melting the scraps is extremelyhigh. In addition, since the area which the scraps S as iron sourcecontact with the molten iron in which the scraps S are melted can bemade small, the molten iron can be super heated and it is possible tosolve the problem which result when the temperature of the molten ironbeing tapped, is low.

[0106] Subsequently the second embodiment will be described withreference to FIG. 8 through FIG. 10. FIG. 8(a) is a plan view showing anarc-melting equipment relating to the second embodiment of the presentinvention. FIG. 8(b) is a sectional view taken on line X-X′ of FIG.8(a).

[0107] According to this embodiment as shown in FIGS. 8(a) and 8(b), aportion corresponding to the preheat shaft of the melting chamber and apart of a bottom of a portion corresponding to the separating distanceportion, constitute a slant portion 1 c, which locates slantwise at ahigher position gradually from the position of 1 d (the deepest positionat a bottom of a portion 1 b). In this case, the bottom (1 d) moveshigher toward the tilting direction, when the furnace tilts. The tappingportion 3 is placed in the slant portion(1 c) in the melting chamber.Therefore, the tapping portion (15) moves toward the deepest position,when the furnace is tilting.

[0108] As shown in FIG. 9 and FIG. 10, by tilting the melting furnace 1,the area where scraps contact with molten iron 8 turns from the slantline portion 8 a of FIG. 9 to the slant line portion of FIG. 10. And dueto the existence of the slant portion 1 c, the area where the scrapscontact with the molten iron 8, becomes remarkably smaller than that ofthe first embodiment. Super heat (ΔT) of the molten iron can, therefore,be increased, as compared with the first embodiment. And it is possibleto more effectively avoid the problem that occur when the temperature ofthe molten metal being tapped is low. After overheating is carried outin this manner, the operation is the same as in the first embodiment.Thus, the scraps S are continuously maintained in the melting furnace 1and the preheat shaft 2 by further tilting the melting furnace 1, thestopper 16 which has closed the tapping hole 15 is moved upward to openthe tapping hole 15. And then one charge of molten iron is tappedthrough the tapping hole 15 into a ladle.

[0109] It should be noted that the arc-melting equipment can beconstituted as shown in FIG. 11. According to the arc-melting equipmentof FIG. 11, a portion directly under the preheating shaft 2 forms aslant portion 18 which slants toward a bottom portion of an separationdistance a. By providing the slant portion 18 in this manner, followingthe melting of the scraps S in contact with the molten iron 8 the scrapsS can be fed more smoothly from the preheat shaft 2 to the separatingdistance portion a.

[0110] The present invention is not limited to the above describedembodiment but can be variably modified. In the above describedembodiment, for example, the tapping portion 3 is arranged facing so asto make a right angle with the direction wherein the scraps flow infacing from a side 1 a of the preheat shaft of the melting furnace 1 tothe opposite side 1 b. It is, however, not limited to the embodiment,and any direction will do so long as the direction is other than thedirection wherein the scraps flow in. If the direction is other than thedirection wherein the scraps flow in, the effect of preventing thescraps from flowing out to the tapping portion can be obtained.

[0111] In addition, the embodiment gives an example wherein scraps areused as iron source to produce molten iron, but other iron source suchas direct reduced iron is also applicable. It is, of course, applicableto equipment which produces molten iron in addition to molten iron. Inthe above described embodiment, an example wherein an arc electrode istilted to melt scraps, is shown. However, the arc electrode is notalways limited to tilting, but any movement means thereof can beavailable.

[0112] Furthermore, as an apparatus for completely separating molteniron and scraps during tapping or a method thereof such a practicalembodiment as given in the following can be employed. That is to say, amethod as shown in FIG. 32 is raised wherein a temperature-rise chamberis arranged on the opposite side of a preheat chamber putting a meltingchamber between the temperature rise chamber and the preheat chamber,the melting chamber is tilted at the time when a predetermined amount ofmolten iron accumulates in the melting chamber and the molten iron isled to the temperature-rise chamber to completely separate the molteniron and cold iron source in the melting chamber. Furthermore as shownin FIG. 1, there is a method wherein the temperature rise chamber isarranged in the direction different from the direction to which coldiron source from the preheat shaft is fed, the melting chamber is tiltedas shown in FIG. 33 at the time when a predetermined amount of molteniron is accumulated in the melting chamber and the molten iron is led tothe temperature-rise chamber to completely separate the molten iron andcold iron source in the melting chamber. Still furthermore, as shown inFIG. 34 a bottom-up portion is arranged at a bottom portion of a side ofa melting chamber, molten iron is elevated in temperature before themolten iron surface arrives at the bottom-up portion of the meltingchamber and the molten iron is tapped.

[0113] The reference numerals of FIG. 32 are described below.

[0114]802: a melting chamber; 803: a preheat chamber; 807 a: an upperelectrode for arc generation in the melting chamber; 807 b: an upperelectrode for arc generation in the temperature-rise chamber; 810 a and810 b: lances for feeding oxygen; and 811 a and 811 b: a device forblowing coke in.

[0115] The reference numerals of FIG. 33 are described below.

[0116]1007 a and 1007 b: an electrode for arc generation; 1014: slag;1014: molten iron; and 1022: a tapping hole.

[0117] Subsequently referential numerals of FIG. 34 are described below.

[0118]902 c: a bottom-up portion; 903: a preheat chamber; 905 a furnacewall; 906: a furnace cover; 907: furnace bottom electrodes; 908: anupper electrode; 910: a tilting device; 912: a lance for blowing oxygenin; 913: a lance for blowing carbonaceous material in; 914: a burner;915: a tapping hole; 917: supply bucket; 918: cold iron source; 920:molten slag; and 921: an arc.

[0119] In the second embodiment, one example is shown, wherein a slantportion is composed of two sorts of the portions, one corresponds to thepreheating shaft of the melting chamber and the other is a part of thebottom corresponding to an separation distance portion. The whole partof the above described bottom portion, however, may be the slantportion. In the above described embodiment, an example wherein scrapsare used as iron source to produce molten iron is shown, but It isapplicable to apparatus, wherein cold pig iron is used as iron source toproduce molten iron.

[0120] (Embodiment 1)

[0121] Scraps of 150 ton were charged into a melting furnace of a directcurrent arc apparatus as shown in FIG. 1 through FIG. 5, wherein amelting furnace(length : 8.5 m; width : 3 m; height 4 m) is directlyconnected to a preheating shaft(3 m W×3 m D) and an arc was formed inthe melting furnace by a graphite electrode of 28 inches with maximumelectric power source capacity of 600 V, 100 kA to melt the scraps. Inaddition, a water cooled lance was inserted through a working entranceplaced at a furnace side wall and oxygen of 6000 Nm³/hr was fedthere-through. When molten iron accumulated in the furnace, coke wasinjected at a rate of 80 kg/min into slag to start the slag formingoperation and the top end of the graphite electrode was buried in theforming slag. Voltage at this time was set to 400 V. If the scraps inthe preheating shaft descended following melt of the scraps in themelting furnace, additional scraps were fed from an upper part of thepreheating shaft by the bucket 4 for charging scraps to keep a level ofthe scraps at a certain height in the preheating shaft.

[0122] In this manner, the melting was promoted in a state that thescraps were continuously maintained in the melting furnace and in thepreheating shaft. At a stage where 180 tons of molten iron was totallyproduced in the melting furnace, the melting furnace was tilted on thetapping portion side at 15 degrees, a contact area of the molten ironand the scraps was reduced to allow superheating of the molten ironabove its heating point and furthermore the melting furnace was tilted.And 120 tons of molten metal was tapped through a tapping hole into aladle, leaving 60 tons in the furnace. Temperature of the molten iron atthe time of tapping was 1575° C. Carbon concentration in the molten ironwas 0.1%.

[0123] After 120 tons of molten iron was tapped, the melting furnace wasreturned to the state before the tapping. While oxygen feed and the cokeinjection were being carried out, slag forming operation was performedand the melting was continued. When the molten iron in the meltingfurnace amounted again to 180 ton, the melting furnace was tilted againto superheat the molten iron and tapping of 120 ton of the molten ironwas repeated. Molten iron of 120 ton was obtained for time of betweentapping of about 40 minutes on average. Electric power unit consumptionof 175 kWh was obtained by using an oxygen amount of 33 Nm³/t and cokeunit consumption of 26 kg/t.

[0124] The 120 tons of the molten iron which was tapped, was elevated toa temperature of 1620° C. by a ladle furnace(LF), and was continuouslycast to produce a billet of 175×175 mm. Electric power unit consumptionof LF was 45 kWh/t on average.

[0125] On the other hand, with regard to Comparative example (similar toPrior Art 3) which was melted in a single batch,using the sameequipment, without feeding scraps continuously, electric power unitconsumption was also investigated.

[0126] These results were shown in Table 1. As shown in Table 1, Example1 wherein oxygen was continuously fed on condition that oxygenconsumption is substantially equal, showed electric power unitconsumption reduced by about 140 kWh from the consumption of theComparative example, and less by about 125 kWh, even if electric powerunit consumption which is necessary for LF, is included. In addition,even if compared with reported examples of other process whichconventional art showed, the present invention shows that the electricpower unit consumption which is necessary, without considering LF, isless by 50 kWh/t and thus it has been confirmed that preheat efficiencyof scraps according to the present example is very high.

[0127] (Embodiment 2)

[0128] Melting similar to Example 1 was carried out in the abovedescribed melting furnace except that oxygen amount was 45 Nm³/t andcoke unit consumption was 36 kg/t. The results were also shown inTable 1. Electric power unit consumption in this case was extremely lowto show 135 kWh, and molten iron having 1575° C. on average was obtainedfor time of tap to tap of about 37 minutes.

[0129] (Embodiment 3)

[0130] Melting was carried out under conditions similar to that of theabove described Example 1 using a melting furnace and a preheating shaftof a direct arc apparatus, wherein there is a portion corresponding to apreheating shaft of a melting furnace as shown in FIG. 8, FIG. 9 andFIG. 10 a melting furnace (length: 8.5 m; width: 3 m; height: 4 m)directly connected to the preheat shaft (3 m W×3 m D) and a half part ofa bottom portion of a portion corresponding to an separating distanceportion have a slant surface for example of 15 degrees.

[0131] As the results, as shown in Table 1 the tapping temperature inthis case was 1600° C. higher than the temperatures of Example 1 andExample 2. Electric power unit consumption of 188 kWh was obtained byoxygen amount of 33 Nm³/t and coke unit consumption of 26 kg/t, andelectric power unit consumption of LF was 30 kWh/t on average.

[0132] (Embodiment 4)

[0133] Melting similar to Example 3 was carried out in the abovedescribed melting furnace except that oxygen amount was 45 Nm³/t andcoke unit consumption was 36 kg/t. The results were also shown inTable 1. Electric power unit consumption in this case was extremely lowto show 148 kWh, and molten iron having 1600° C. on average was obtainedfor time of tap to tap of about 37 minutes. TABLE 1 Comparative Example1 Example 2 Example 3 Example 4 Example Operation The The The The Batchmethod present present present present Operation invention inventioninvention invention Oxygin 33 45 33 45 33 unit consumpt- ion (Nm3/t)Coke unit 26 36 26 36 26 consumpt- ion (kg/t) Tappig 1575 1575 1600 16001620 temper- ature (° C.) Electric 175 135 188 148 315 power unitconsumpt- ion (kWh/t) LF unit 45 45 35 35 30 consumpt- ion (kWh/t) Total220 180 223 183 345 power unit consumpt- ion (kWh/t)

[0134] Now subsequently another embodiment of the present invention willbe described with reference to FIG. 12 through FIG. 15. FIG. 12 is asectional view showing an arc-melting apparatus relating to anembodiment of the present invention. This arc-melting apparatus isequipped with a material furnace 101 for arc-melting a cold iron source,and a preheating shaft 102 directly connected to an upper portion of themelting furnace. An exhausting portion 102 a, which is connected to anexhaust gas adsorption system, is placed at an upper end of thepreheating shaft 102. Iron scraps 103 as cold iron source are chargedinto the preheat shaft 102.

[0135] Two lances 112 a, 112 b are inserted turning their top ends intosurface of molten iron bath in the melting furnace 101, oxygen beingsupplied through the lance 12 a and coke as supplementary heat sourcebeing injected through lance 112 b. It should be, however, noted that assupplementary heat source carbonaceous material other than the coke maybe also used.

[0136] A tapping hole 114 is formed at a bottom portion of a projectingportion 101 a arranged at a portion different from a side where thepreheat shaft 102 of the melting furnace 101 is directly connected, andat a side end of the tapping hole a slag door 115 is placed. It shouldbe, however, noted that the tapping hole may be placed on the sameperipheral surface with the slag door 115. Into the projecting portion101 a, a burner 113 is inserted from above the projecting portion, whereit is possible to elevate the temperature of molten iron which istapped. In this case, heating means such as an arc electrode or the likecan be installed instead of the burner 113.

[0137] As shown FIG. 12, a side wall of the preheating shaft 102 has ataper which extends downward. By forming such taper high temperature,the scraps can be steadily supplied into molten iron 108 in the meltingfurnace 101. In case that the taper is not formed, the scraps 103 do notslide freely over the wall portion of the preheat shaft 102 so much thatthe scraps do not fall under their own weight, which causes hanged up ofthe scraps.

[0138] Oxygen supplying devices 116 for supplying oxygen to the scraps103, are located at a lower portion of the shaft 102 in the meltingfurnace 101. And in the vicinity of the devices, the scraps arefulfilled. As shown in FIG. 13, six of these supplying devices areinstalled, and by supplying oxygen therefrom to the scraps 103, thescraps can be cut off into smaller size, simultaneously with beingmelted. By cutting off the scraps 103, simultaneously with melting inthis manner, state of hanging up is prevented more effectively.

[0139] It should be noted that in case where oxygen is supplied throughthe oxygen supply devices 116 the oxygen gas may be supplied alone orother gas may be mixed with the oxygen gas. Oxygen compound gas may beused so long as it will support combustion.

[0140] In addition, as shown in FIG. 14, a fuel supply device 117 forsupplying fuel such as oil and gas can be installed together with theoxygen supply devices. By supplying fuel in this manner, the scraps 103can be more easily cut off by being melted.

[0141] When the iron scraps are melted in the melting equipmentconstituted in this manner, the scraps 103 are firstly charged into themelting furnace 101 and the preheat shaft 102 to form a combustion,whereby the iron scraps 103 are continuously maintained in the meltingfurnace and in the preheat shaft 102.

[0142] In this state an arc 107 is formed by an arc electrode 106, theiron scraps 103 are melted and simultaneously the oxygen is suppliedfrom the oxygen supply devices 116 to cut off the scraps 103 by melting.

[0143] In case that the fuel supply device 117 is installed, the fuelsuch as oil is supplied together with the oxygen. In case that theoxygen is supplied to the scraps 103 in this manner, the scraps 103 arepreheated by the burning fuel to high temperature, whereby the scraps103 are cut off by melting. Owing to this, even if the scraps 103 pileat a portion thereof which remain as not yet melted in a lower portionof the preheating shaft 102, since the scraps are cut off, hanging-upcan be prevented. Although as described above, by forming the taper onthe preheating shaft 102, hanging-up is reduced. Some hanging-up ofscraps in the preheating shaft occurs to some extent of frequency. Sincethe scraps 103 at a lower part of the preheating shaft 102 are cut offin this manner, hanging-up is almost completely prevented from beingcaused by the piling of the scraps at the not yet melted portionthereof.

[0144] At the time of melting the scraps 103 by the arc 107, the oxygenis supplied through the lance 112 a into the furnace to assist thescraps 103 to be melted. When molten iron is accumulated in the furnace,coke is injected as supplementary heat source through the lance 112 binto slag continue the slag forming operation and a top end of theelectrode 106 is buried in slag 109 so that the arc 107 is formed in theslag 109. This coke which has been injected as supplementary heat sourcereacts with the oxygen which has separately been supplied to generate COgas and simultaneously the reaction heat contributes to melting thescraps 103.

[0145] In addition the oxygen which has been supplied through the oxygensupply devices 116 reacts with iron to form FeO, and this FeO is alsoreduced by coke which has been supplied through the lance 112 b.

[0146] Melting of the scraps progresses and when the molten iron of forexample one charge or more is accumulated in the furnace, the furnace istilted to elevate the temperature for a predetermined time. And whilethe scraps are continuously maintained in the melting furnace 101 andthe preheating shaft 102, the melting furnace 101 is tilted to tap themolten iron of one charge from the tapping hole 114 into a ladle or thelike. At the time of the tapping, in order to prevent the tapping hole114 from being blocked by solidification of the molten iron, the molteniron may be heated by the burner 113.

[0147] As described above, from a standpoint of melting the scrapsefficiently, it is preferable to use supplementary heat source such ascoke and by supplying oxygen through the different lance 112 a as wellas injecting coke as supplementary heat source through the abovedescribed lance 112 b CO gas is generated to be able to produce heat. Inthis case total amount of oxygen which is supplied from the lance 112 aand the oxygen supply device 116 is preferably 25 Nm³/t or more. Owingto this, the scraps can be more efficiently melted. More preferably thetotal amount of oxygen is 40 Nm³/t.

[0148] If the melting is performed in this manner under conditionswherein the scraps are maintained in contact with the molten iron, sincetemperature of the molten iron is low to be approximately1550° C., thereis the possibility that the tapping hole 114 is blocked by partialsolidification of the molten iron. As described above, however, byheating the molten iron by the burner 113, such problem can be avoided.Of course, for the purpose other means for heating such as an arcelectrode can be employed.

[0149] (Embodiment 5)

[0150] Scraps of 150 tons were charged into a melting furnace and apreheating shaft of a direct current arc apparatus, wherein the meltingfurnace (furnace diameter: 7.2 m; height: 4 m) is directly connected tothe preheating shaft(5 m W×3 m D×7 m H), and as shown in FIG. 13 oxygen,supplying devices(oxygen supplying nozzles) 116 are installed at sixplaces and an arc was formed by a graphite electrode of 30 inches withan electric power source capacity of maximum 750 V, 130 kA to melt thescraps. In addition, a water cooled lance was inserted through a workingentrance placed at a furnace side wall to supply oxygen at a rate of4000 Nm³/hr there-through. When molten iron has accumulated in thefurnace, coke was injected at a rate of 80 kg/min into slag to continuethe slag forming operation and the top end of the graphite electrode wasburied in the forming slag. Voltage at this time was set to be 550 V.When the scraps in the preheating shaft descended the following melt ofthe scraps in the melting furnace, the scraps were supplied from abucket for charging the scraps at an upper part of the preheating shaftto keep a level of the scraps at a certain height in the preheatingshaft.

[0151] During this time, oxygen was supplied through the above describedoxygen supplying devices (oxygen supplying nozzles) at a rate of 350˜500Nm³/hr per nozzle to the scraps at a lower part of the preheating shaft102 to melt and cut the scraps 103. And by preventing the hanging-up ofscraps in the furnace, a stable state was maintained whereby the scrapscontinuously fall into the molten iron.

[0152] In this manner, the melting is promoted under conditions wherethe scraps were continuously maintained in the melting furnace and inthe preheating shaft. At a stage where 180 tons of molten iron wasproduced, the furnace was tilted to elevate temperature thereof by archeating for a predetermined time. Therefore, 120 tons of molten iron wastapped from the tapping hole into a ladle, leaving 60 tons in thefurnace for continuing the molten process. Temperature of the molteniron at the tapping time was 1550° C. Carbon concentration in the molteniron was 0.1%. The molten iron in the vicinity of the tapping hole washeated by an oxygen-oil burner.

[0153] Even after the molten iron of 120 tons was tapped, the meltingwas continued and when the molten iron amounted again to 180 tons in themelting furnace tapping the molten iron of 120 tons was repeated. Themolten iron (120 tons) was obtained by time with a tap to tap time ofabout 40 minutes on average. Electric power unit consumption of 170kWh/t was obtained by total oxygen amount of 33 Nm³/t from the oxygensupply nozzles and the water cooled lance and coke unit consumption of26 kg/t.

[0154] In case that oxygen was not supplied through the oxygen supplyingnozzles installed at a lower part of the preheating shaft, the scrapswere piled on a portion of scraps which remained as not melted at alower part of the preheating shaft, and the scraps did not drop in thefurnace in spite of there being space on the whole surface of thescraps. The condition of so-called hanging-up continued for a long timeand it resulted in stagnated melting about once per 6 charges (6 numbersof the tapping time). According to the present invention, however, byactively melting and cutting off the scraps by means of supplying oxygenthrough the oxygen supplying nozzles at a lower part of the preheatingshaft, such a stagnation of melting did not occur.

[0155] Tap to tap time and its frequency, which is in the case scrapswere melted and cut off by supplying oxygen, compared with in the casescraps were not melted and not cut off by oxygen(in the case oxygen wassupplied at a rate of 6000 Nm³/hr , exclusively through a water cooledlance) are shown in FIG. 15. As seen apparently from FIG. 15, in casethat oxygen was not supplied, it has been confirmed that supply ofscraps was delayed and it has also been confirmed that as the resultsthere existed charge wherein tap-tap time was long. However, in casethat cutting was performed by oxygen, it has been confirmed that in anycharge was taken the tap-tap time of about 40 minutes.

[0156] Subsequently another embodiment of the present invention will bedescribed with reference to FIG. 16 through FIG. 18. FIG. 16 is asectional view showing an arc-melting apparatus, which relates to anembodiment of the present invention. This arc-melting apparatus cannotalways prevent the in-furnace hanging-up of scraps effectively, becausethe friction force of its wall surface and scraps 203 is large, when thepreheating shaft is rectangular, even when a taper is given to thepreheating shaft 202. In order to prevent the in-furnace hanging-up ofscraps, it is preferable that the sectional shape of the preheatingshaft is circular, an ellipse or a curve.

[0157] In a range from the surface position of the molten iron bath inthe melting furnace 201 to an upper end position of scraps of thepreheating shaft 202, plural stages (3 stages in the drawing) of gasintroduction entrances 216, for supplying oxygen containing gas such asoxygen gas and air to a portion where scraps are charged, are installed.By the oxygen containing gas, which is introduced from the gasintroduction entrances 216, CO gas generated in the melting furnace ismade to burn.

[0158] In such a way, by installing a plurality of gas introductionentrances at arbitrary positions in the range, which is, from thesurface position of the molten iron bath in the melting furnace 201 toan upper end position of scraps of the preheating shaft 202, CO gasgenerated from the melting furnace 201 can be made to burn at a pluralof the arbitrary positions in a scraps layer in the melting furnace 201and a scraps layer 202 in the preheating shaft 202. For example, onethird of the entire combustion amount at a scraps layer in the meltingfurnace 201, one third thereof at a scraps layer in a lower part of thepreheating shaft 2 directly above the melting furnace 1 and the rest onethird thereof at a medium position between the surface of the molteniron bath in the preheating shaft 2 and the highest position of thescraps can be made to burn. Since, therefore, the whole amount of CO isnot made to burn at one position, temperature of the combustion gas doesnot become high and the dissociation of CO₂ by O₂ took into CO isprevented. In addition, since CO is made to burn at a position which isdesired, it is well controllable and it can be made to burn surely andefficiently.

[0159] As shown in FIG. 17, these gas introduction entrances 216 areplaced in plurality (4 places in FIG. 17) in number in peripheraldirection per one stage. Two stages or more of these gas introductionentrances are preferably formed at a position lower than 0.5 L, where Lis the length or distance from the surface of the molten iron bath inthe melting furnace 201 to an upper end position of cold iron source atan upper part of the shaft. If the position is higher than 0.5 L, theheat transfer time after burning is short, and the effect is small. Ifone stage is formed, combustible gas becomes high in temperature andthere is possibility that problems that scraps are oxidized and thatheat load to equipment is too high. Furthermore these gas introductionentrances exist preferably with 5 stages or less at the position lowerthan 0.5 L. In case that the gas introduction entrances with 6 stages ormore are installed at a position lower than 5 L, reversibly distancewhere oxygen containing gas such as air goes into the preheat shaft isreduced, burning at a center portion of the preheat shaft 2 is delayed,gas which has not yet burnt burns at a position higher than 0.5 L andefficiency is lowered.

[0160] According to the present embodiment, since a plurality of gasintroduction entrances 216 are installed at arbitrary positions in arange from molten iron bath surface position in the melting furnace 1 toan upper end position of scraps of the preheating shaft 202, by blowingoxygen containing gas such air and oxygen gas through these gasintroduction entrances 216, CO gas generated from the melting furnace201 can be made to burn at plural arbitrary positions in a scraps layerin the melting furnace 201 and a scraps layer 203 in the preheatingshaft 202. As opposed to the situation where CO is made to burn at oneposition of a scraps layer 203, using plural portion avoids that thetemperature of combustible gas is too high resulting in the scrapsbecoming fused and in the dissociation of CO₂, which had been producedby burning gases in O₂. In addition, since CO is made to burn at aposition which is desired, burning is well controlled so that it can bemade to burn surely and efficiently, and the heat thereof can beeffectively used for preheating the scraps.

[0161] In this case, total blow amount of oxygen containing gas ispreferably made so that oxygen amount Qin which is calculated fromoxygen concentration in the total blow amount of oxygen containing gasand flow rate has the following formula (A) with respect to reactionwith supplementary heat source and with respect to oxygen amountQ(Nm³/min) which is blown in the furnace to oxidize metal.

0.55Q≦Qin≦0.9Q  (A)

[0162] This is because if Qin is over 0.9 Q, oxygen which does not takepart in burning remains along with surplus N₂ and results in increaseddrop in temperature of generated gas, thereby lowering efficiency.Furthermore, there is an increased problem of oxidation caused by thesurplus oxygen, because on the other hand, if Qin is less than 0.55 Q,the whole amount of generated CO cannot to be made to burn and CO whichhas not burnt will exist at an upper part of the shaft.

[0163] Subsequently another embodiment of the present invention will bedescribed with reference to FIG. 16 through FIG. 19.

[0164] According to the above described embodiment, the substantiallywhole part of CO exhaust gas which was generated in the melting furnace201 was made to burn by an oxygen containing gas from gas introductionentrances which were installed with plural stages at arbitrary positionsin the range from molten iron bath surface position in the meltingfurnace 201 to an upper end position of scraps of the preheat shaft 202.According to the present embodiment, however, a slag door 215 of themelting furnace 201 is made to work as a working door for having airenter into the melting furnace 201, this working door 215 is openedduring melt treatment to have air enter into the melting furnace and apart of the CO exhaust gas which has not yet burnt is made to burn inthe melting furnace 201. And then the rest of the CO exhaust gas whichhas not yet burnt is made to burn by an oxygen containing gas from gasintroduction entrances which are installed at arbitrary positions in therange from molten iron bath surface position in the melting furnace 201to an upper end position of scraps of the preheat shaft 202.

[0165] If air is introduced into the melting furnace 201 in this manner,a part of high temperature CO gas which has been generated in thefurnace burns in the entering air, but since the burning occurs in themelting furnace 201, the burning does not result in locally hightemperatures in a layer of scraps which have not yet been melted andfusion of the scraps does not occur. In addition, this burning heattransfers the heat to the scrap 203 between the molten iron surface andan lower end position of the preheat shaft 202 before exhaust gas entersinto the preheat shaft 202, and the burning heat lowers to temperatureswhere local fusion does not occur when the exhaust gas enters into thepreheat shaft 202. Furthermore, since the heat of the gas transfers heatto the scraps even in the preheat shaft 202, the temperature of theexhaust gas is not high and the fusion of the scraps does not occur evenin the preheat shaft 202. The scraps of that part can be efficientlypreheated. And the transfer of heat of the exhaust gas to the scraps 203is ensured in this manner so that the heat is effectively used forpreheating the scraps 203.

[0166] According to the present embodiment, when a part of the COexhaust gas burns in the entering air in the melting furnace 201, the COgas which has not yet burnt burns in the melting furnace 1, so that ODis less than 0.7, if CO₂/(CO₂+CO) is made to be OD. If the value of ODis 0.7 or more, heating value in the furnace becomes so large thatdamage to the furnace and fusion of scraps occur. It is more preferablethat OD is less than 0.6.

[0167] In the above-mentioned way, according to the present embodiment,a part of the non-combustible CO gas is made to burn in the meltingfurnace 201. Therefore, compared with an embodiment, wherein there isburning at only one position of a scraps layer in this embodiment, thereis no possibility that the temperature of the combustible gas will be sohigh as for the scraps to be fused, or for the O₂ to be produced bydissociation of CO₂, which has been produced by burning. In addition,since CO is made to burn at a position which is desired, burning is wellcontrolled so that it can be made to burn surely and efficiently and theheat can be used effectively for preheating the scraps.

[0168] The present embodiment is different from other embodiments. Asshown in FIG. 18, according to the present embodiment, a part of the COexhaust gas has already burned in the melting furnace 201. One stage ofthe gas introduction entrance 216 may be satisfactory. Of course,plurality of stages of the gas introduction entrances may also besatisfactory. As in the same way as other embodiments, from a standpointof increasing efficiency of preheating the scraps 203, it is preferablethat the gas introduction entrance 216 is located preferably at a lowerpart.

[0169] In the case where there is one stage of gas introduction entrance216, and where gas introduction amount is small even if there areplurality of stages of gas introduction entrances, the value of OD ispreferably more than 0.3. If the value of OD is 0.3 or less, the heatingvalue of gas in the preheating shaft 2 is so short that the scrapscannot be sufficiently preheated. It is more preferable that OD is morethan 0.4.

[0170] Since even according to the present embodiment, in the same wayas conventional embodiment the scraps 203 are supplied so that thescraps 203 are continuously maintained in the melting furnace 201 and inthe preheating shaft 202, efficiency of preheating the scraps by exhaustgas is high. By detaining 40% or more of scraps of one chargecontinuously in the melting furnace 201 and the preheat shaft 202 duringmelting and at the tapping time, efficiency of preheating becomesextremely high. In addition, CO gas is generated by reacting withsupplementary heat source such as coke and the oxygen supply used foroxidation of metal for slag forming. This oxygen supply amount ispreferably 25 Nm³/t or more as well. It is more preferable that theoxygen supply amount is 40 Nm³/t.

[0171] (Embodiment 6)

[0172] Scraps (150 tons) were charged into a melting furnace and apreheating shaft of a direct current arc apparatus, wherein the meltingfurnace (furnace diameter: 7.2 m; height : 4 m) is directly connected tothe preheat shaft(5 m W×3 m D×7 m H). And an arc was formed by agraphite electrode of 28 inches with an electric power source capacityof maximum 600 V, 100 kA, to melt the scraps. In addition, a watercooled lance was inserted through a working entrance placed at a furnaceside wall for supplying oxygen at a rate of 6600 Nm³/hr there-through.

[0173] As shown in FIG. 19, nozzles (gas introduction entrances) 216 forblowing air into the melting furnace 1 and the preheating shaft 2 areinstalled at 9 stages. That's to say, this 9 number of stages comprises,as the total result of one stage (A) having 4 places, at a side wallabove the molten iron bath surface in the melting furnace 1 (lower by1.5 m from an upper end of the melting furnace) and further 8 stages (B,C, D, E, F, G, H & I) having respectively 4 places, from a positionlower by 500 mm from the shaft at the preheat shaft 202. Through each ofthe nozzles, air was blown in, in amounts as shown in Table 2. Andelectric power unit consumption and a gas constituent of an upper partof the preheating shaft were measured at the same time.

[0174] Furthermore, after the molten iron accumulated in the furnace,the coke was injected at a rate of 80 kg/min into slag, in order todrive the slag forming operation. And then, the top end of the graphiteelectrode was buried in the forming slag. Voltage at this time was setto be 400 V. In order to keep the level of scraps at a predeterminedheight in the preheating shaft, as the scraps in the preheating shaftdropped into the melting furnace, additional scraps were supplied intothe preheating shaft from a bucket for charging the scraps into an upperpart of the preheating shaft.

[0175] In this way, the melting is promoted under the condition that thescraps were continuously maintained in the melting furnace and thepreheating shaft. When 180 tons of molten metal was produced in themelting furnace, 120 tons was tapped from the tapping hole into a ladle,leaving 60 tons in the furnace. Temperature of the molten iron at thetapping time was 1550° C. Carbon concentration in the molten iron was0.1%. The molten iron in the vicinity of the tapping hole was heated byusing an oxygen-oil burner.

[0176] Even after the 120 tons of molten steel was tapped, oxygen supplyand coke injection continued, slag forming operation continued and themelting continued. When the molten iron amounted again to 180 tons inthe melting furnace, tapping of 120 tons of molten iron was repeated.The results of Table 2 show an average value of 5 numbers of chargeswhich repeated this melting. It should be noted that Example 1 through 9in the Table 2 were within the scope of the present invention andComparative examples 1 through 4 were out of the scope of the presentinvention. In Comparative examples 1 through 3, the melting furnace wasshut tightly, in Examples 1 and 2 air blow was performed with one stageand in Comparative example 3, air blow was not performed. In addition,in Comparative example 4, conventional operation by batch was performed.

[0177] According to the results of the Table, it has been confirmed thatin Examples in which scraps are always maintained in the melting furnaceand the preheat shaft and where CO gas which has not yet burnt can burnefficiently, efficiency of preheating the scraps is high and electricpower unit consumption can be reduced. Above all, in Examples 1, 2 and 4wherein the location of air blow and an amount of air blow wereparticularly in a preferable range, molten iron of 120 tons was obtainedbetween tappings in about 40 minutes on average, electric power unitconsumption of 175 to 180 kWh was possible when the oxygen amount of 33Nm³/t and coke unit consumption was 26 kg/t. Electric power unitconsumption was therefore lowered by 60 to 120 kWh/t in comparison withComparative examples 1 through 4 to which the present invention did notapply.

[0178] The molten iron (120 tons) which had been tapped was elevated toa temperature of 1620° C. by a ladle furnace (LF) to produce a billet of175×175 mm by continuous casting. TABLE 2 Example Comparative example 12 3 4 5 6 7 8 9 1 2 3 4 Secondary combustion 380 380 380 381 381 380 240480 480 380 380 0 0 air (Nm3/min) Air blowing position A 190 127 120 160120 380 and blowing amount B 190 190 127 127 120 160 120 380 (Nm3/min.)D 190 127 127 127 160 120 F 190 127 127 120 H 190 127 Electric powerunit 175 180 220 180 195 210 230 215 225 250 240 280 300 consumption(kWh/t) Coke unit consumption 26 26 26.2 26.1 26 26.3 25.8 29.2 29.131.9 30 26 26 (kg/t) Tap-Tap (min) 40.1 40.5 44.5 40.5 42 43.1 45.5 44.145 46.5 46.2 48.9 — Exhausting gas CO (%) 0.4 0.5 2.8 0.35 0.55 2.4 32.50 0.1 0.4 0.4 42 — composition CO2 (%) 99.2 99 93.3 99.3 99 94.3 67.5 7977.5 99.3 99 52.3 — (Excluding N2 content) O2(%) 0.4 0.5 3.9 0.35 0.453.3 0 21 22.4 0.3 0.6 5.7 — Remarks Batch type

[0179] (Embodiment 7)

[0180] In the above described melting furnace, the same melting as thatof Example 1 was performed, except that the supplied oxygen amount was9500 Nm³/hr, coke was 120 kg/min, oxygen amount was 45 Nm³/t and cokeunit consumption was 36 kg/t. The air blow position, the air blowcondition and the results are shown in Table 3. Examples 10 through 18of the Table 2 were within the scope of the present invention andComparative examples 5 through 8 were out of the scope of the presentinvention. In Comparative examples 5 through 7 the melting furnace wasshut tightly, in Comparative examples 5 and 6 air blow was performed byone stage and in Comparative example 7 air blow was not performed. Inaddition, in Comparative example 8 operation by batch was performed.

[0181] From the results of Table 3, according to the present embodiment,it has been confirmed as follows.

[0182] Since the scraps are always maintained in the melting furnace andthe preheating shaft and CO gas which has not yet burnt can be made toburn efficiently, efficiency of preheating the scraps is high andelectric power unit consumption can be reduced. Above all, in Examples10, 11 and 14, wherein a position of air blow and an amount of air blowwere particularly in a preferable range, molten iron of 120 tons wasobtained from tapping to tapping in about 37 minutes on average,electric power unit consumption of 120 kWh/t was obtained by oxygenamount of 45 Nm³/t and coke unit consumption of 36 kg/t and electricpower unit consumption was lowered by 80˜150 kWh/t, in comparison withComparative examples 5 through 8 to which the present invention did notapply. TABLE 3 Example Comparative example 10 11 12 13 14 15 16 17 18 56 7 8 Secondary combustion 570 570 570 570 570 570 570 360 720 570 570 00 air (Nm3/min) Air blowing position A 285 190 180 570 and blowingamount B 285 285 190 190 180 180 570 (Nm3/min.) C 285 285 190 190 180180 E 285 190 190 180 G 285 190 I 285 190 Electric power unit 120 120140 175 120 150 170 185 200 200 240 245 270 consumption (kWh/t) 36.1 3636 36.2 35.9 36 36.2 39 42.2 42 36 26 37 Coke unit consumption 37 37.138.2 40 37 38.5 39.5 40.5 43.5 43 46.1 48.9 (kg/t) Tap-Tap (min) 37 37.138.2 40 37 38.5 39.5 40.5 43.5 43 46.1 48.9 — Exhausting gas CO (%) 0.450.45 0.5 0.55 0.45 0.45 0.55 33.5 0.1 0.42 0.53 41 — composition CO2 (%)99.2 99.15 99.1 99 99.15 99.15 99 66.5 77.4 99.3 99.12 53.5 — (ExcludingN2 content) O2 (%) 0.35 0.4 0.4 0.45 0.4 0.4 0.45 0 22.5 0.28 0.35 5.5 —Remarks Batch type

[0183] (Embodiment 8)

[0184] Scraps of 150 tons were charged into a melting furnace and apreheating shaft of a direct current arc apparatus, wherein the meltingfurnace (furnace diameter: 7.2 m; height: 4 m) is directly connected tothe preheating shaft (5 m W×3 m D×7 m H) and an arc was formed by agraphite electrode of 28 inches with an electric power source capacityof maximum 600 V, 100 kA to melt the scraps. In addition, a water cooledlance was inserted through a working entrance placed at a furnace sidewall to supply oxygen at a rate of 9500 Nm³/hr there-through.

[0185] As shown in FIG. 18, a gas introduction entrance 216 forintroducing air as oxygen containing gas to a lower part of a preheatingshaft 202 was installed at one stage (at 4 places), and further amountof entering air into the melting furnace 201 was made adjustable by theworking door 215. And then, air was supplied through the working door215 and the gas introduction entrance 216 to burn CO. Totalpost-combustion air amount and values of OD(=CO₂/(CO₂+CO)) at respectivepositions at that time are shown in Table 4. In addition, electric powerunit consumption and gas constituent at an upper part of the preheatshaft at that time were measured.

[0186] At the time when the molten iron had accumulated in the furnace,coke was injected at a rate of 120 kg/min into slag to drive the slagforming operation, and the top end of the graphite electrode was buriedin the forming slag. The voltage at this time was set to be 400 V. Asthe scraps in the preheating shaft descended following melt of thescraps in the melting furnace, additional scraps were supplied from abucket for charging the scraps from an upper part of the preheatingshaft to keep a level of the scraps at a predetermined height in thepreheating shaft.

[0187] In this manner, the melting is promoted under conditions wherescraps were continuously maintained in the melting furnace and thepreheating shaft, and at a stage where molten iron of 180 tons wasproduced in the melting furnace, 120 tons for one charge was tapped fromthe tapping hole into a ladle, leaving 60 tons of molten iron in thefurnace. Temperature of the molten iron at the time of tapping was 1550°C. Carbon concentration in the molten iron was 0.1%.

[0188] The molten iron in the vicinity of the tapping hole was heated byan oxygen-oil burner.

[0189] Even after 120 tons of molten iron was tapped while oxygen supplyand coke injection were being performed, slag forming operation wasperformed and the melting was continued. When the molten iron amountedagain to 180 tons in the melting furnace, tapping 120 tons of molteniron was repeated. The results of Table 4 show an average value of 5charges which repeated this melting and tapping cycle. It should benoted that Example 19 in the Table 13 is within the scope of the presentinvention and Comparative example 9 is out of the scope of the presentinvention. In Comparative example 9 OD in the melting furnace shows 0.7or more.

[0190] From the results of Table 4, it has been confirmed that inExample 19, efficiency of preheating the scraps is high enough to beable to reduce electric power unit consumption. According to thisinventive Example, molten iron of 120 tons was obtained with a tappingto tapping time of 40 minutes on average, and electric power unitconsumption of 175 kWh/t was obtained by oxygen amount of 36 Nm³/t andcoke unit consumption of 26 kg/t. On the other hand, according toComparative example 9, electric power unit consumption was, a littlebit, lower than that of Example 19. However, a lot of troubles onapparatus and a lot of troubles on operation such as fusion, frequentlyoccurred in the Comparative example 9. TABLE 4 Comparative Example 19example 9 In-furnace CD 0.5 0.85 (═CO2/CO2 + CO) Secondary combustionair 190 60 Electric power unit 175 170 consumption(Kwh/t) Coke unitconsumption(kg/t) 26 26 Tap-Tap (min) 40 40 Exhausting gas combustion(excluding N2 content) CO(%) 0.4 0.3 CO2(%) 99.2 99.4 O2(%) 0.4 0.3Remarks Furnace cover is damaged to a large extent Occurrence of scrapfusion

[0191] Subsequently, another embodiment of the present invention will bedescribed with reference to FIG. 20 and FIG. 21 of the presentinvention. According to the present embodiment, a slag door 315 of amelting furnace 301 is the working door for introducing air into themelting furnace 301, and air is introduced into the melting furnace 301by opening this working door 315 during melting treatment to burn a partof the CO exhaust gas which has not yet burnt in the melting furnace301. And then, the rest of the CO exhaust gas which has not yet burnt ismade to burn by oxygen containing gas from a gas introduction entrance316, which is placed in the area between the molten iron bath surfaceposition and the upper end position of the scraps in the preheatingshaft.

[0192] In this manner, if air is introduced into the melting furnace301, a portion of high temperature CO gas which has been generated inthe furnace is made to burn by the introduced air. But since the burningoccurs in the melting furnace 301, it does not become high locally intemperature within a layer of the scraps which have not yet been meltedand fusion of the scraps does not occur. In addition, heat of this gastransfers to the scraps 303 between the surface of the molten iron bathand the lower end position of the preheating shaft 302 before theexhaust gas enters into the preheating shaft 302 and its temperature, islowered sufficiently to avoid local fusion of scraps when the exhaustgas enters into the preheat shaft. Furthermore, since heat of the gastransfers to the scraps 303 the temperature of the exhaust gas is nothigh when the rest of CO gas is made to burn in the vicinity of theupper end surface of the scraps in the preheat shaft 302 and therefore,local fusion does not occur at that portion, either. According to theabove described embodiment, since CO gas is made to basically burn at aportion wherein the scraps exist there is some possibility that scrapsfuse, but the present embodiment can substantially prevent the scrapsfrom fusing.

[0193] In addition, the position of the gas introduction entrance 316 isappropriately arranged to adjust the supply amount of oxygen containinggas and to adjust the combustion ratio at the melting furnace 301. Thispoints the temperature of the exhaust gas in the vicinity of the exit ofthe preheat shaft 302 namely at a portion of an exhaust portion 302 canbe controlled to be a predetermined temperature or more. Furthermore, byrapidly cooling the exhaust gas thereafter, the occurrence of injurioussubstances such as aromatic chlorine compound which is represented bydioxin and occurrence of white smoke and malodor can be prevented.

[0194] According to the present embodiment, CO gas which has not yetburnt is made to burn in the melting furnace 301 so that OD is less than0.7 at the time when a portion of CO exhaust gas is made to burn byentering air in the melting furnace, where CO₂/(CO₂+CO) is made to beOD. If the value of OD is 0.7 or more, the remaining CO amount is sosmall that even if the rest of CO is made to burn at the upper-mostportion of the preheat shaft 2, the temperature of the exhaust gascannot be made to be sufficiently high (e. g. a temperature of 750° C.or more) to decompose the above described injurious substances. Thevalue of OD is more preferably made to be less than 0.6.

[0195] In this way, according to the present embodiment, a portion of COin the oxygen containing gas is burnt in the melting furnace 301.Therefore, as well as burning in one position of the scrap layer 316,the temperature of the burning gas is so high that the fusion of thescraps 303 can surely be prevented, comparing with the above-describedembodiment. Furthermore, there is no possibility to generate O₂ by thedissociation of CO₂. In addition, since the amount of CO which burns byintroducing air into the melting furnace and the amount of CO whichburns by blowing oxygen containing gas into the scraps 303 can becontrolled, and since oxygen containing gas can be supplied to a desiredposition of the scraps 303 with a desired amount, the temperature of theexhaust gas in the vicinity of the exit of the preheat shaft 302 is wellcontrolled at a predetermined temperature or more, to burn surely withhigh efficiency.

[0196] In addition, as shown in FIG. 21 according to the presentembodiment, since a portion of the non-combustible CO exhaust gas in themelting furnace 301 has already been burnt by oxygen in the meltingfurnace, the gas introduction at entrance 316 may be composed of onestage. Of course it may be composed of plurality of stages. Similarly toconventional embodiment, in order to arise the temperature of theexhaust gas at an exhaust portion 302 a to a predetermined temperatureor more, the gas introduction entrance 316 is preferably installed inthe vicinity of an upper end surface of the preheat shaft 302. Morespecifically, the gas introduction entrance 316 is preferably formed atleast in the space from an upper surface of the scraps of the preheatshaft 302 and a lower position by 2 m therefrom.

[0197] In this manner in case that the gas introduction entrance 316 iscomposed of one stage and in case that gas introduction amount is smalleven if the gas introduction entrance 316 is composed of plurality ofstages, the value of OD is preferably more than 0.3. In such a case ifthe value of OD is 0.3 or less, heat of gas is so low that it isimpossible to sufficiently preheat the scraps. The value of OD is morepreferably more than 0.4.

[0198] Even according to the present embodiment, melting of the scrapsprogresses and when a predetermined amount of molten iron accumulates,while maintaining the scraps continuously in the melting furnace 301 andthe preheat shaft 302, the furnace is tilted to tap the molten iron forone charge through the tapping hole 314 into a ladle. Therefore, thescraps can be similarly preheated to temperature higher than in theconventional melting equipment.

[0199] Furthermore, since the scraps 303 are supplied to the preheatshaft 302 so that the scraps 303 are continuously maintained in themelting furnace 301 and in the preheat shaft 302, efficiency ofpreheating the scraps by the exhaust gas is high. By continuouslymaintaining at least the scraps of 50% of one charge in the meltingfurnace 301 and in the preheat furnace 302 during melting and at time oftapping, efficiency of preheating becomes extremely high.

[0200] Furthermore, in addition, CO gas is generated by reaction with asupplementary heat source such as coke and the oxygen supplied amountfor slag forming is also preferably 25 Nm³/t or more as well. It is morepreferably 40 Nm³/t.

[0201] (Embodiment 9)

[0202] Scraps (150 tons) were charged into a melting furnace and apreheating shaft of a direct current arc apparatus, wherein the meltingfurnace (furnace diameter: 7.2 m; height: 4 m) is directly connected tothe preheating shaft (5 m W×3 m D×7 m H) and an arc was formed by agraphite electrode of 28 inches with an electric power source capacityof maximum 600 V, 100 kA to melt the scraps. In addition, a water cooledlance was inserted through a working entrance placed at a furnace sidewall to supply oxygen at a rate of 9500 Nm³/hr there-through.

[0203] As shown in FIG. 22, nozzles (gas introduction entrances) 316 forblowing air into the melting furnace 1 and in the preheating shaft 2were installed at 6 stages in total at one stage(A) with 4 places at aside wall above molten iron bath surface in the melting furnace 301(lower by 1.5 m from an upper end of the melting furnace) and furtherrespectively at 5 stages(B, C, D, E & F) with 4 places at an interval,as shown in the figure from a position lower by 500 mm from the shaft atthe preheating shaft 202. Through each of the nozzles air was blown inas allocated as shown in Table 31 and electric power unit consumption,the temperature of the exhaust gas at an upper part of the preheatingshaft was measured as was the occurrence of injurious substances such asdioxin and the occurrence of white smoke and malodor accompaniedthereby.

[0204] When molten iron accumulated in the furnace, coke was injected ata rate of 120 kg/min into slag to drive slag forming operation, and thetop end of the graphite electrode was made to be buried in the formingslag. The voltage at this time was set to be 400 V. When the scraps inthe preheat shaft descended following melt of the scraps in the meltingfurnace, additional scraps were supplied from a bucket for charging thescraps from an upper part of the preheat shaft to keep the level of thescraps at a certain height in the preheat shaft.

[0205] In this manner, the melting is promoted while the scraps werecontinuously maintained in the melting furnace and in the preheat shaft.When 180 tons of the molten iron was produced in the melting furnace and60 tons of molten iron where maintained in the furnace and the 120 tonswas tapped from the tapping hole into a ladle, the temperature of themolten iron at the time of the tapping was 1550 ° C. Carbonconcentration in the molten iron was 0.1%.

[0206] The molten iron in the vicinity of the tapping hole was heated byan oxygen-oil burner.

[0207] Even after the molten iron of 120 tons was tapped, the oxygensupply and coke injection were continued along with slag formingoperations and the melting was continued. When the molten iron amountedagain to 180 tons in the melting furnace, 120 tons of the molten ironwere again tapped. The results of Table 31 show an average value of 5charges which repeated this melting. It should be noted that Examples 1through 3 in the Table 31 were within the scope of the present inventionand Comparative examples 1 through 3 were out of the scope of thepresent invention. In any one of Comparative examples 1 through 3,temperature of the exhaust gas was low at the exit of the shaft. InComparative example 3 the melting furnace was shut tightly and air wasnot blown.

[0208] From the results of Table 5 it has been confirmed thattemperature of the exhaust gas at the exit of the shaft can be raised to900° C. or more, that therefore, occurrence of injurious substances suchas dioxin can be made to be substantially zero and the occurrence of thewhite smoke and the malodor can be avoided. In contrast to this, in eachof Comparative examples wherein temperature is low at the exit of theshaft, the injurious substance is frequently produced, and the whitesmoke and the malodor is also produced.

[0209] In addition, it has been confirmed that as shown by the inventiveExamples, when the scraps are continuously maintained in the meltingfurnace and in the preheat shaft, and CO gas which has not yet burnt ismade to post-combust, efficiency of preheating the scraps is high andelectric power unit consumption can be lowered. In these Examples themolten iron(120 tons) was obtained in a time between tapping of 37minutes on average, electric power unit consumption of 140˜150 kWh/t wasobtained by oxygen amount of 45 Nm³/t and coke unit consumption of 36kg/t, electric power unit consumption was low by 80 kWh/t in comparisonwith Comparative example 3 wherein air blow was not performed.

[0210] The molten iron of 120 tons which had been tapped was elevated totemperature of 1620° C. by a ladle furnace(LF) to produce a billet of175×175 mm by continuous casting. TABLE 5 Example Comparative example 12 3 1 2 3 Secondar combustic air (Nm3/Min) 570 570 570 570 570 0 Airblowing position A 285 & blowing amount (Nm3/Min) B 285 190 C 285 190190 D 285 190 E 190 F 285 285 190 Electric power unit consumption(kWh/t) 155 170 170 130 140 240 Coke unit consumption (kg/t) 36.1 36 3636.2 35.9 36 Tap-Tap (min) 37 37.3 37.6 36.2 37 48.6 Temperature ofexhausting gas 955 960 925 320 395 125 at the exit of the shaft (° C.)White smoke, Malodor Not found Found Harmful matter as Dioxin1/500-1/1500* 1

[0211] (Embodiment 10)

[0212] Scraps of 150 tons were charged into a melting furnace and apreheat shaft of a direct current arc equipment wherein the meltingfurnace(furnace diameter: 7.2 m; height : 4 m) is directly connected tothe preheat shaft(5 m W×3 m D×7 m H) and an arc was formed by a graphiteelectrode of 28 inches with an electric power source capacity of maximum600 V, 100 kA to melt the scraps. In addition, a water cooled lance wasinserted through a working entrance placed at a furnace side wall tosupply oxygen at a rate of 9500 Nm³/hr there-through.

[0213] As shown in FIG. 21, a gas introduction entrance 316 for blowingair as oxygen containing gas into a space between an upper end surfaceof the scraps of the preheat shaft 302 and a position lower by 2 mtherefrom is installed at one stage(with 4 places) and furthermoreamount of the entering air into the melting furnace 301 is made by aworking door 315 to be adjustable. And then air was supplied through theworking door 315 and the gas introduction entrance 316 to burn CO. Totalamount of post-combustion air and values of OD(=CO₂/(CO₂+CO) atrespective positions are shown in Table 6. In addition, electric powerunit consumption, the temperature of the exhaust gas at an upper part ofthe preheat shaft, the occurrence state of injurious substances such asdioxin and the occurrence state of white smoke and malodor accompaniedthereby were investigated.

[0214] When molten iron accumulated in the furnace, coke was injected ata rate of 120 kg/min into slag to drive slag forming operation, and thetop end of the graphite electrode was buried in the forming slag. Thevoltage at this time was set to be 400 V. When the scraps in the preheatshaft descended following melt of the scraps in the melting furnace,additional scraps were supplied from a bucket for charging the scrapsfrom an upper part of the preheat shaft to maintain the level of thescraps at a predetermined height in the preheat shaft.

[0215] In this manner, the melting is promoted in a state that thescraps were continuously maintained in the melting furnace and in thepreheat shaft. When 180 tons of the molten iron was produced in themelting furnace, 120 tons was tapped from the tapping hole into a ladle,leaving 60 tons in the furnace. The temperature of the molten iron atthe time of the tapping was 1550° C. Carbon concentration in the molteniron was 0.1%.

[0216] The molten iron in the vicinity of the tapping hole was heated byan oxygen-oil burner.

[0217] Even after the molten iron of 120 tons was tapped, oxygen supplyand coke injection were continued as was the slag forming operation, andthe melting was continued. When the molten iron amounted again to 180tons in the melting furnace, tapping of 120 tons of the molten iron wasrepeated. The results of Table 6 show an average value of 5 chargeswhich repeated this melting. It should be noted that inventive Example 4in the Table 6 was within the scope of the present invention andComparative examples 4 through 6 were out of the scope of the presentinvention. In Comparative example 4 ,OD in the melting furnace is 0.7 ormore, and in Comparative example 5 wherein the melting furnace was shuttightly and air was not blown through the gas introduction entrance, thetemperature of the exhaust gas at the exit of the shaft was low.

[0218] From the results of Table 6 ,it has been confirmed that inExample 4, the temperature of the exhaust gas at the exit of the shaftcan be increased to 900° C. or more, the occurrence amount of theinjurious substance such as dioxin can be reduced substantially to zeroand the white smoke and the malodor can be prevented. In contrast tothis, in each of the Comparative examples 4 and 5 wherein temperature islow at the exit of the shaft, injurious substance has frequently beenproduced, and white smoke and malodor have also occurred.

[0219] In addition, it has been confirmed that because the scraps aremaintained continuously in the melting furnace and in the preheat shaftfor the inventive examples, CO gas which has not yet burnt can be madeto post-combust and efficiently preheat the scraps, while electric powerunit consumption can be lowered. In these Examples, 120 tons of themolten iron was obtained whereby a time between tapping of 37 minutes onaverage, electric power unit consumption was reduced to 140˜150 kWh/t,when oxygen was injected in an amount of 45 Nm³/t and coke unitconsumption was at 36 kg/t. This is an electric power unit consumptionwhich is lower by 80 kWh/t in comparison with Comparative example 5wherein air injection was not used. The 120 tons of molten iron whichhad been tapped was elevated to temperature of 1620° C. by a ladlefurnace(LF) to produce a billet of 175×175 mm by continuous casting.TABLE 6 Comparative example Example 4 4 5 Secondary combustion air 570570 0 (Nm3/min) OD(═CO2/CO2 + CO)) Inside of the melting Furnace 0.6 0.80.4 Center of the preheating shaft 0.6 0.8 0.8 Exit of the reheatingshaft 1 1 1 Electric power unit 155 140 240 consumptior(kWt/t) Coke unitconsumption (kg/t) 36.1 36.2 36 Tap-Tap (min) 37 36.2 48.6 Temperatureof the shaft exit (° C.) 955 350 125 White smoke, Malodor Not foundFound Found Harmful matter as dioxin 1/500-1/1500* 1 1 Fusion PhenomenonNot found Not Not found found

[0220] Another embodiment of the present invention will now be describedwith reference to FIG. 23 of the present invention. In the foregoingdescribed embodiment, a plurality of gas introduction entrances 416 wereinstalled at random positions in a range from a molten iron bath surfaceposition in a melting furnace 401 to an upper end position of scraps ofa preheat shaft. These gas introduction entrances 416 are optional. Inthe case that the gas introduction entrances 416 are not installed, COgas which has not yet burnt is made to entirely burn in apost-combustion chamber 417. Alternatively a pipe through which CO gaswhich has not yet burnt is introduced to the post-combustion chamber 417is arranged and a portion of gas which has not yet burnt may be suppliedto the post-combustion chamber 417 without passing through a preheatshaft 1.

[0221] (Embodiment 11)

[0222] Scraps of 150 tons were charged into a melting furnace and apreheating shaft of a direct current arc apparatus, wherein the meltingfurnace(furnace diameter: 7.2 m; height: 4 m) is directly connected tothe preheat shaft (5 m W×3 m D×7 m H) and an arc was formed by agraphite electrode of 28 inches with an electric power source capacityof maximum 600 V, 100 kA to melt the scraps. In addition, a water cooledlance was inserted through a working entrance placed at a furnace sidewall to supply oxygen at a rate of 9500 Nm³/hr there-through.

[0223] As shown in FIG. 23, nozzles(gas introduction entrances) 416 forblowing air into the melting furnace 401 and the preheating shaft 402were installed at 5 stages in total at one stage(A) with 4 places at aside wall above molten iron bath surface in the melting furnace 401(lower by 1.5 m from an upper end of the melting furnace) and furtherrespectively at 4 stages(B, C, D & E) with 4 places at an interval asshown in the figure from a position lower by 500 mm from the shaft atthe preheat shaft 402 and furthermore a nozzle (a gas introductionentrance) 418 was installed at a position of an upper part(F) of apost-combustion chamber 417 which was connected to an exhaust portion402 a of the preheat shaft 402. Through each of the nozzles, apredetermined amount of air was blown in as shown in Table 7 and theelectric power unit consumption, the temperature of the exhaust gas atan upper part of the preheat shaft, and the occurrence of the injurioussubstances such as dioxin and the occurrence state of white smoke andmalodor accompanied thereby at that time, were measured.

[0224] As the molten iron accumulated in the furnace, at time ofmelting, coke was injected at a rate of 120 kg/min into slag to drivethe slag forming operation, and the top end of the graphite electrodeburied in the forming slag. The voltage at this time was set to be 400V. When the level of scraps in the preheat shaft lowered followingmelting of the scraps in the melting furnace, additional scraps weresupplied from a bucket for charging the scraps into an upper part of thepreheat shaft to keep the level of the scraps at a predetermined heightin the preheat shaft.

[0225] In this manner, the melting is promoted under conditions wherethe scraps were continuously maintained in the melting furnace and thepreheat shaft. When 180 tons of molten iron was produced in the meltingfurnace, 120 tons were tapped,leaving 60 tons of the molten iron in thefurnace. The 120 tons of iron for one charge, was tapped from thetapping hole into a ladle. Temperature of the molten iron at the time ofthe tapping was 1550° C. Carbon concentration in the molten iron was0.1%.

[0226] The molten iron in the vicinity of the tapping hole was heated byan oxygen-oil burner.

[0227] Even after the molten iron of 120 tons was tapped, oxygen supply,coke injection, slag forming operation and the melting were continued.When 180 tons of the molten iron accumulated in the melting furnace,tapping of 120 tons of the molten iron was repeated. The results ofTable 1 show an average value of 5 charges which repeated this melting.It should be noted that Examples 1 through 3 in the Table 1 were withinthe scope of the present invention and Comparative examples 1 through 3were out of the scope of the present invention. In each one ofComparative examples 1 through 3, wherein post-combustion was notperformed, the temperature of the exhaust gas at the exit of the shaftwas low. In Comparative example 3, the melting furnace was shut tightlyand air injection was not performed.

[0228] From the results of Table 6, it has been confirmed that inExamples of the present invention, the temperature of the exhaust gaswhich is discharged from the post-combustion chamber increased to 900°C. or more, whereby the amount of the injurious substance such as dioxincan be reduced substantially to zero and white smoke and malodor can beeliminated. In contrast to this, in each of the Comparative examples,wherein temperature is low at the exit of the shaft, injurioussubstances are frequently produced, and white smoke and malodor occur.

[0229] In addition, it has been confirmed that because the scraps arealways maintained in the melting furnace and in the preheating shaft forthe inventive example, CO gas which has not yet burnt can be made topost-combust efficiency and efficiently preheat the scraps, whileelectric power unit consumption can be lowered. In these Examples, 120tons of the molten iron was obtained, with a time between tapping of 37minutes on average, electric power unit consumption of 140˜150 kWh/t wasobtained when oxygen was injected in an amount of 45 Nm³/t and coke unitconsumption was at 36 kg/t. This is an electric power unit consumptionwhich is lower by 80 kWh/t in comparison with Comparative example 3wherein air injection was not used.

[0230] The 120 tons of molten iron which had been tapped was elevated totemperature of 1620° C. by a ladle furnace(LF) to produce a billet of175×175 mm by continuous casting. TABLE 7 Example Comparative example 12 3 1 2 3 Secondar combustic air (Nm3/Min) 570 570 570 570 570 0 Airblowing position A 285 & blowing amount (Nm3/Min) B 285 190 C 285 190190 D 285 190 E 190 F 285 285 190 Electric unit consumption (kWh/t) 155170 170 130 140 240 Coke unit consumption (kg/t) 36.1 36 36 36.2 35.9 36Tap-Tap (min) 37 37.3 37.6 36.2 37 48.6 Temperature of exhausting gas935 940 905 320 395 125 at the exit of the shaft (° C.) White smoke,Malodor Not found Found Harmful matter as Dioxin 1/500-1/1500* 1

[0231] (Embodiment 12)

[0232] An Example which uses iron scraps and DRI (carbon concentration:1.5 wt %) of direct reduction iron together in a direct current arcfurnace, as shown FIG. 24 will be described here-below. The arc furnacehas a melting chamber of a furnace diameter: 7.2 m; a height: 4 m, apreheating chamber of a width: 3 m; a length: 5 m; a height: 7 m and afurnace capacity of 180 tons. First changed into the melting chamberwere 30 tons of DRI at a normal temperature and 50 tons of iron scrapsat a normal temperature, subsequently 70 tons of iron scraps at a normaltemperature were charged into the preheating chamber. Melting was begunusing an upper electrode made of graphite with a diameter of 30 inchesand using an electric power source of maximum 750 V, 130 KA. As themolten iron was produced, quick lime and fluorite were added to formmolten slag and subsequently oxygen gas was blown in at a rate of 4000Nm³/hr through an oxygen gas blow lance and coke was blown in at a rateof 50 kg/min through a carbonaceous material blow lance into the moltenslag. By blowing in oxygen gas and coke the molten slag was formed and atop end of the upper electrode was buried in the molten slag. Voltage atthis time was set to be 520˜550 V.

[0233] After this DRI was continuously charged at a rate of 1.8 tons/mininto the melting chamber and the melting was continued. In addition, asiron scraps in the preheating chamber descended following the melting,iron scraps were charged by a supply bucket into the preheating chamberto maintain the level of the iron scraps at a predetermined height asthe melting continued. When 180 tons of molten iron was produced in themelting chamber, the charge of DRI into the melting chamber was stoppedand the DRI was allowed to completely melt. Molten iron (120 tons) forone charge was tapped into a ladle, leaving 60 tons behind in themelting chamber. At the tapping the molten iron was heated by a heavyoil burner. Carbon concentration of the molten iron at the time of thetapping was 0.1 wt %, and temperature of the molten iron was 1560° C.

[0234] After the tapping a tapping hole was filled up with filling sandand thereafter a charge of DRI and injection of oxygen gas and coke werecontinued. When the molten iron amounted to 180 tons again the tappingthe molten iron of 120 tons was repeated. The molten iron after beingtapped was refined by a ladle refinery furnace, elevated to atemperature of 1620° C. and cast by a continuous caster. The electricpower consumption at the ladle refinery furnace was 50 kWh/t on average.

[0235] With the combination ratio of DRI of 70%, the time from tappingto tapping was 65 minutes on average, with an oxygen gas blow amount of33 Nm³/t, coke blow amount of 25 kg/t and the electric power unitconsumption by 535 kWh/t for the melting to be accomplished. Totalelectric power consumption by the arc furnace and the ladle refineryfurnace was 585 kWh/t.

[0236] In addition, in order to make comparison, in the arc furnace asshown in FIG. 24, 30 tons of DR1 of a normal temperature were chargedinto the melting chamber, subsequently 36 tons of iron scraps at anormal temperature were charged into the preheating chamber and themelting was begun. When molten iron was produced direct reduction ironof 54 tons was continuously charged without additionally charging ironscraps to obtain 120 tons of molten iron and after this molten ironelevated to a temperature of 1600° C., a tapping operation comparativeexample 1) was also performed. Oxygen gas blow amount and coke blowamount in Comparative example 1 were the same as those of the abovedescribed Example 12, and in addition, the electric power unitconsumption in the ladle refinery furnace was 30 kWh/t. Operationconditions and operation results in Example 12 and Comparative example 1are shown in Table 8. TABLE 8 Comparative Example 1 example 1 Iron scrapsupplying method to All the time, Per heat to preheating Furnace fillingup Oxygen-gas blowing amount (Nm3/t) 33 33 Carbonacious material blowingamount(kg/t) 25 25 Tapping temperature(° C.) 1560 1600 Electric powerunit consumption (kWh/t) Arc Furnace 535 595 Ladle refinary 50 30furnace Total unit 585 625 consumption

[0237] As shown in Table 8, in Comparative example 1, the electric powerunit consumption in the arc furnace was 595 kWh/t and total electricpower unit consumption of an arc furnace and a ladle finery furnace was625 kWh/t. In this manner according to Example 1 of the presentinvention, electric power of about 40 kWh/t in terms of total unitconsumption could be reduced in comparison with Comparative example 1.

[0238] (Embodiment 13)

[0239] Example 2 which uses iron scraps and cold iron( carbonconcentration: 4.5 wt %) together in a direct current arc furnace willbe described here-below. The arc furnace has a melting chamber of afurnace diameter: 7. 2 m; a height: 4 m, a preheating chamber of awidth: 3 m; a length: 5 m; a height: 7 m and a furnace capacity of 180tons.

[0240] First charged into the melting chamber were 30 tons of cold ironat a normal temperature and 50 tons of iron scraps at a normaltemperature, subsequently 70 tons of iron scraps at a normal temperaturewere charged into the preheating chamber and melting was begun using anupper electrode made of graphite with a diameter of 30 inches and usingan electric power source of maximum 750 V, 130 KA. As molten iron wasproduced, quick lime and fluorite were added to form molten slag andsubsequently oxygen gas was blown at a rate of 6000 Nm³/hr through anoxygen blow lance and coke was blown at a rate of 80 kg/min through acarbonaceous material blow lance into the molten slag. By blowing oxygengas and coke the molten slag was formed and a top end of the upperelectrode was buried in the molten slag. Voltage at this time was set tobe 550 V.

[0241] After this, as iron scraps in the preheating chamber descendedfollowing the melting, iron scraps were charged by a supply bucket intothe preheating chamber to maintain the level of the iron scraps at adetermined height as the melting continued. When 180 tons of molten ironwas produced, 120 tons of molten iron for one charge was tapped into aladle, leaving 60 tons behind in the melting chamber. At the tapping themolten iron was heated by a heavy oil burner. Carbon concentration ofthe molten iron at the time of the tapping was 0.1 wt %, and temperatureof the molten iron was 1560° C.

[0242] After the tapping, the tapping hole was filled up with fillingsand and thereafter 30 tons of cold iron of a normal temperature wasdirectly charged into the melting chamber and at the same time oxygengas and coke were injected. When molten iron amounted to 180 tons again,the tapping 120 tons of the molten iron repeated. The molten iron afterbeing tapped was refined in a ladle refinery furnace, elevated to atemperature of 1620° C. and thereafter cast by a continuous caster. Theelectric power consumption at the ladle refinery furnace was 60 kWh/t onaverage.

[0243] As a result of a combination of the use of cold iron at 25%, atime from tapping to tapping of 40 minutes on average, an oxygen gasblow amount of 33 Nm³/t, a coke blow amount of 16 kg/t and an electricpower unit consumption of 195 kWh/t, the melting could be performed.Total electric power consumption was 255 kWh/t by the arc furnace andthe ladle refinery furnace.

[0244] In addition, in order to make comparison, 30 tons of cold iron ata normal temperature and 20 tons of iron scrap at a normal temperaturewere charged into the melting chamber, subsequently 70 tons of ironscraps of a normal temperature were charged into the preheating chamberand melting was begun. Molten iron (120 tons) was obtained withoutadditionally charging iron scraps into the preheating chamber and afterthis molten iron was elevated to a temperature of 1590° C. tappingoperation(Comparative example 2) and a mixture of iron scraps and coldiron(hereinafter referred to as “mixture A”) in which combination ratioof cold iron was 25% was charged into the preheating chamber melting,was begun. When the mixture A in the melting chamber melted anddescended, additional mixture A was charged into the preheating chamberto maintain a level of the mixture A at a predetermined height, whilethe melting was continued. At the time when 180 tons of molten iron wasproduced in the melting chamber, 120 tons for one charge was tapped,leaving about 60 tons behind in the melting chamber. The melting andtapping operation was repeated (Comparative example 3). Oxygen gas blowamount and coke blow amount in Comparative example 2 and Comparativeexample 3 were the same as those of the above described Example 2. Inaddition, the electric power unit consumption on average in the ladlerefinery furnace was 30 kWh/t according to Comparative example 2 and 60kWh/t according to Comparative example 3. Operation conditions andoperation results in Example 2, Comparative example 2 and Comparativeexample 3 are shown in Table 9. TABLE 9 Operational condition and itsresults Comparative Comparative Example 1 example 2 example 3 Iron scrapsupplying All the time Per heat All the time method to fillig up filligup to preheating Furnace Supplying method for cold Direct DirectSupplying by Iron source supplying supplying way of to melting tomelting preheating chamber chamber furnace Oxygen-gas (Nm3/t) 33 33 33Carbonacous material 16 16 16 blowing amount (kg/t) Tappingtemperature(° C.) 1560 1590 1560 Tap-Tap time(min) 40 45 43 Electricpower unit consumption (kWh/t) Arc Furnace 195 310 180 Ladle refinary 6030 60 furnace Total unit 255 340 240 consumption Occurrence ratio out ofthe 0.8 0.8 3.1 constitution (%)

[0245] As shown in Table 9, according to Comparative example 2, theelectric power unit consumption in the arc furnace was 310 kWh/t and thetotal unit consumption of an electric power by the arc furnace and aladle finery furnace was 340 kWh/t. Thus, the electric power unitconsumption was increased by 85 kWh/t, in comparison with Example 2 ofthe present invention. In addition, since in Comparative example 3 coldiron was preheated, the electric power unit consumption was decreased by15 kWh/t, in comparison with the inventive example 2. However, inComparative example 3, by spending time in adjusting carbonconcentration before tapping time, the tapping to tapping time wasextended by 3 minutes, and at the same time the occurrence amount of outof requirement with respect to carbon concentration of molten iron afterhaving been tapped, was high, in comparison with the inventive example2. The occurrence amount was 3.1%, which was almost 4 times,incomparison with that of Example 2. In this manner, according to Example2 of the present invention, not only an electric power unit consumptioncould be reduced but also the product which is out of specification withrespect to carbon concentration was small, making a stable operationpossible.

[0246] Next another embodiment of the present invention will bedescribed with reference to FIG. 26 and 27.

[0247] (Embodiment 14)

[0248] An example in an arc furnace which is shown in FIG. 25 and FIG.26 will be described here-below. The arc furnace has a melting chamberof a furnace diameter: 7.2 m; a height: 4 m, a preheating chamber of awidth: 3 m; a length: 5 m; a height: 7 m and a furnace capacity of 180tons. First charged into the preheating chamber, were 70 tons of ironscraps at a normal temperature, subsequently 40 tons of cold iron(carbonconcentration: 4.5 wt %) and 50 tons of iron scraps at a normaltemperature were charged into the melting chamber. Melting was begunusing an upper electrode made of graphite with a diameter of 30 inchesand using an electric power source of maximum 750 V, 130 KA. Inaddition, immediately after electric current was turned on quick limeand fluorite were added and at the same time oxygen was blown at a rateof 6000 Nm³/hr through an oxygen blow lance and coke was blown at a rateof 36 kg/min through a carbonaceous material blow lance into the meltingchamber. The quick lime and the fluorite were heated and by blowingoxygen and coke the molten slag was formed. A top end of the upperelectrode was buried in the molten slag. Voltage at this time was set tobe 550 V. Thereafter as iron scraps in the preheating chamber descendedas a result of melting, additional iron scraps were charged by a supplybucket into the preheating chamber to maintain a level of the ironscraps at a certain height while the melting continued. When molten 180tons of molten iron was produced, 120 tons was tapped into a ladle,leaving about 60 tons of molten iron behind in the melting chamber. Attapping the molten iron was heated by a heavy oil burner. Carbonconcentration of the molten iron at the time of the tapping was 0.1 wt%, and temperature of the molten iron was 1560° C. After the tapping 40tons of molten iron was charged again into the melting chamber andsubsequently the injection of oxygen and coke was restarted when themolten iron again amounted to 180 tons, the tapping of 120 tons of themolten iron was repeated. The molten iron after being tapped was refinedby a ladle refinery furnace, elevated to a temperature of 1620° C., andthereafter cast by a continuous caster. The electric power consumptionat the ladle refinery furnace was 60 kWh/t on average.

[0249] The results shows that melting can be accomplished with acombination ratio of molten iron: 33%, oxygen blow amount: 33 Nm³/t andcoke blow amount: 12 kg/t, time from tapping to tapping of 40 minutes onaverage and an electric power unit consumption of 80 kWh/t. Totalelectric power consumption by the arc furnace and the ladle refineryfurnace was 140 kWh/t.

[0250] In addition, for comparison, 70 tons of iron scraps at a normaltemperature were charged into the preheating chamber, subsequently 40tons of molten iron(carbon concentration: 4.5 wt %) and 10 tons of ironscraps at a normal temperature were charged into the melting chamber andmelting was begun. In this case, molten iron (120 tons) was obtained,without additional charging iron scraps, continuing the melting. Afterthe molten iron was elevated to a temperature of 1600° C. the molteniron was tapped. (Comparative Example, Inventive Example). In this case,oxygen gas blow amount and coke blow amount in the Comparative example,were the same as those of the above inventive Example. In addition, inthe Comparative Example, the electric power unit consumption in theladle refinery furnace was 30 kWh/t. Operation conditions and operationresults for the inventive Example and for the Comparative example areshown in Table 10. TABLE 10 Operational condition and its resultsComparative Example example Iron scrap supplying All the time Per heatmethod to fillig up to preheating furnace Oxygen-gas blowing amount 3333 (Nm3/t) Carbon blowing 12 12 amount (kg/t) Tapping temperature(° C.)1560 1600 Tap-Tap time(min) 40 60 Electric power unit consumption(kWh/t) Arc Furnace 80 240 Ladle refinary 60 30 furnace Total unit 140270 consumption

[0251] As shown in Table 10, according to the Comparative example anelectric power unit consumption in an arc furnace was 240 kWh/t, totalunit consumption of an electric power by an arc furnace and a ladlefinery furnace was 270 kWh/t and in addition, time from tapping totapping was 60 minutes on average. However, following the Example of thepresent invention, total electric power consumption could be reduced by130 kWh/t in comparison with Comparative example and at the same time,the tapping to tapping could be shorten by 20 minutes.

[0252]FIG. 29 shows an electric power unit consumption in an arc furnaceaccording to an example which varies combination ratio of molten iron to20˜45% on condition that oxygen blow amount of 33Nm³/t is constant. Asshown in FIG. 4, it has been found that with an increase in the amountof molten iron, the electric power unit consumption decreases and thatif the combination ratio of the molten iron is made to be about 50% ormore the arc furnace can be operated solely by the heat of burning thecarbon in the molten iron without using electric power.

[0253] Now subsequently another embodiment of the present invention willbe described with reference to FIG. 30 and FIG. 31.

[0254] The present invention will be described with reference to thedrawings herein-after. FIG. 30 is a longitudinally sectional schematicview of an-arc melting equipment which shows one example of anembodiment of the present invention.

[0255] In FIG. 30, a shaft type preheating chamber 703 and a furnacewall 704 with a water cooling structure are arranged at an upper part ofa melting chamber 702 which is internally constructed with refractory.The melting chamber 702 is equipped with furnace bottom electrodes 706at bottom and an upper opening of the furnace wall 704, which is notcovered with the preheating chamber 703, is covered with a furnace cover705 having a water cooling structure which can be freely opened andclosed. An upper electrode 707 made of graphite which is movable up anddown is arranged passing through this furnace cover 705, and a base ofan arc-melting equipment 701 is constructed. The furnace bottomelectrodes 706 and the upper electrode 707 are connected to a directcurrent power source(not shown) and an arc 719 is produced between thefurnace bottom electrodes 706 and the upper electrode 707.

[0256] At an upper part of the preheating chamber 703 a hopper typesupply bucket 715 is provided hanging up on a travelling truck 724, andfrom this supply bucket 715 cold iron source 716 such as iron scraps anddirect reduction iron is charged via a supply opening 720 which can befreely opened and closed into the preheating chamber 703. A duct 721placed at an upper end of the preheating chamber 703 is connected to adust collector (not shown). High temperature exhaust gas which isgenerated in the melting chamber passes through the preheating chamber703 and the duct 721 in sequence to be absorbed and the cold iron source716 in the preheating chamber 703 is preheated, thereby. The cold ironsource 716 which has been preheated falls down into the melting chamberwith dead load corresponding to amount of the cold iron source 716 whichis melted in the melting chamber and thereby the preheated cold ironsource is charged into the melting chamber 702.

[0257] The side wall of the preheating chamber 703 has a taper whichextends downward. By providing the taper the cold iron source 716 whichhas been preheated can be supplied stably to the melting chamber 702. Ifthe taper is not formed, the cold iron source 716 does not fall smoothlyand can hang up in the preheating chamber 703. This taper is preferablyin a range from 2.5˜7 degrees. If the taper is less than 2.5 degrees, itis impossible to effectively prevent hanging up in the preheatingchamber 3. On the other hand, if it is over 7 degrees, the charge amountof the cold iron source 716 in the preheating chamber 703 is reduced andit is impossible to control the time for which the cold iron source 716stays in the preheating chamber 703 to be sufficiently long to obtainsufficient preheating.

[0258] The oxygen blow lance 708 and the carbonaceous material blowlance 709 which are movable up and down in the melting chamber 2 arearranged passing through the furnace cover 705. Oxygen is injectedthrough the oxygen blow lance 708 into the melting chamber 702 andcarbonaceous material such as coke, char, coal, charcoal, graphite isblown through the carbonaceous material blow lance 709 into the meltingchamber 702 using air and nitrogen as carrier gas.

[0259] On the opposite side of a part where the preheating chamber 703of the melting chamber 702 is arranged, there are (i) at the furnacebottom, a tapping hole 713 in which filling sand or mud agent is filledwith an exit side being pressed by a door 722 and (ii) at the side walla slag discharge hole 714 in which filling sand or mud agent is filledwith an exit side being pressed by a door 723. A burner 710 is fittedinto the furnace cover 705 which is a part corresponding to an upperpart perpendicular to this tapping hole 713. The burner 710 burns fossilfuel such as heavy oil, kerosene, pulverized coal, propane gas andnatural gas in the air or oxygen or oxygen enriched air in the meltingchamber 702.

[0260] A tuyere 712 is provided as gas supply means for blowing oxygenor inert gas into the melting chamber 702. The tuyere 712 is arranged ata furnace bottom of the melting chamber 702 in the vicinity of boundaryof the cold iron source 716 which is supplied from the preheatingchamber 703 and the molten iron 717 which is produced in the meltingchamber 702. When oxygen is to be blown in, the tuyere 712 is made of adouble tube structure to form a structure in which cooling gas such aspropane is made to flow through an outer tube. When inert gas such as Aris to be blown in, the tuyere 712 may be made of a single tube, and maybe one which many small tubes of about 1 mm in diameter are puttogether. Alternately, a porous brick may be used in place of the tuyere712. Anyone of those described in the foregoing will do.

[0261] The method of melting cold iron source 716 in an arc-meltingequipment 701 which is constituted in this manner is carried out asfollows. First, from the supply bucket 715, the cold iron source 716 ischarged into the preheating chamber 703. The cold iron source 716 whichhas been charged into the preheating chamber 703 is also charged intothe melting chamber and it fills up the inside of the preheating chamber703. Since the cold iron source 716 is charged uniformly into themelting chamber 702, the cold iron source 716 can also be charged intothe melting chamber 702 on the opposite side of the preheating chamber703 by opening the furnace cover 705.

[0262] Subsequently while oxygen or inert gas is being blown in, directcurrent is being supplied between the furnace bottom electrodes 706 andthe upper electrode 707 to make the upper electrode 7 move up and down,and an arc 719 is generated among the upper electrode 707, the furnacebottom electrodes 706 and the cold iron source 716 which has beencharged. The cold iron source 716 is melted by arc heat which isgenerated to produce molten iron 717. The molten iron is produced and atthe same time flux such as quick lime and fluorite is charged into themelting chamber 702 to form molten slag 718 over the molten iron 717,whereby not only is oxidization of the molten iron 717 prevented butalso the molten iron 717 is kept warm. In case that the molten slag 718is too much in amount, it can be discharged through the slag dischargehole 714.

[0263] In addition, as the melting progress is, if the cold iron source716 piles up in the vicinity of boundary of the cold iron source 716,which piles at a lower position of the preheating chamber 703 and themolten iron 717, the molten iron 717 is stirred by oxygen and inert gaswhich is blown in through the tuyere 712. Since the cold iron source 716which has piled is melted by the molten iron 717 which has been stirred,the cold iron source 716 can be prevented from hanging up.

[0264] From about the time when the molten iron 717 is produced, oxygenand carbonaceous material are blown preferably through the oxygen blowlance 708 and the carbonaceous material blow lance 709 into the molteniron 717 or the molten slag 718. The carbonaceous material which ismelted in the molten iron 717 or the carbonaceous material which issuspended in the molten slag 718 reacts with oxygen to generate heat ofcombustion, which works as supplementary heat source to save electricpower consumption. At the same time, CO gas as a product of reactionmakes the molten slag 718 formed, whereby invites, what is called, slagforming operation in which the arc 719 is wrapped in the molten slag.Therefore, heat transfer efficiency of the arc 719 goes up. In addition,high temperature CO gas which is generated in a large quantity and CO₂gas which is generated by combustion of this CO gas,preheat the coldiron source 716 efficiently in the preheating chambers 703. Blow amountof this carbonaceous material is determined in response to blow amountof oxygen. That is to say, carbonaceous material almost equal tochemical equivalent of oxygen which is blown in is introduced. If theamount of carbonaceous material which is blown in is small in comparisonwith oxygen blow amount, the molten iron is excessively oxidized. Inaddition, oxygen which is blown in through a tuyere 712 reacts with themolten iron to form FeO, but this FeO is reduced by carbonaceousmaterial which has been blown in. In this case the total amount ofoxygen which is blown in through the oxygen blow lance 708 and thetuyere 712 is preferably 25 Nm³ or more per ton molten iron 717 which ismelted, and it is more preferably 40 Nm³ or more. By this the cold ironsource 716 can be more efficiently melted.

[0265] Accompanied by production of the molten iron 717 the cold ironsource 716 in the preheating chamber 3 drops into the melting chamber702 to be reduced, under its own weight, in response to the amount whichis melted in the melting chamber. In order to make up for this reducedamount the cold iron source 716 is charged into the preheating chamber703 from the supply bucket 715. This cold iron source 716 is chargedcontinuously or intermittently into the preheating chamber 703 so thatthe cold iron source 716 is continuously maintained in the preheatingchamber 703 and in the melting chamber 702. In that case in order toincrease preheat efficiency amount of the cold iron source 716 which ismaintained in the preheating chamber 703 and in the melting chamber 702is preferably made to be 40% or more of the cold iron source 716 for onecharge.

[0266] In this manner, the cold iron source 716 is melted until onecharge of molten iron 717 is at least accumulated in the meltingchamber. Therefore, maintaining the cold iron steel 716 continuously inthe melting chamber 702 and in the preheating chamber 703, the meltingchamber 702 is tilted to tap the molten iron 717 for one charge from thetapping hole 713 into a molten iron hold vessel (not shown) such as aladle. At the time of tapping, in order to avoid problems such as theclosing of the tapping hole 713 due to a fall of molten irontemperature, the molten iron 717 may be heated by a burner 710.

[0267] And after the tapping the molten iron 717 is elevated totemperature by the ladle refinery furnace, depending on requirement, itis cast by a continuous caster. After the molten iron 717 is tapped andthe molten slag 718 is discharged, the melting chamber 702 is returnedto horizontal, and filling sand or mud agent is put up in the tappinghole 713 and the slag discharge hole 714. Subsequently an electriccurrent is turned on again and the melting is continued. Since as fornext heating the melting can be begun with the cold iron source 716which has been preheated, efficiency of melting is improved. At the timeof tapping, leaving the molten iron 717 of several dozens of tons behindin the melting chamber 702 the melting for next charge may be started.By doing this, initial melting is promoted and efficiency of melting isfurther improved.

[0268] By heating and melting the cold iron source 716 in this manner,the cold iron source 716 can be prevented from hanging-up at a lowerposition of the preheating chamber 703 in the melting chamber 702 andefficient and stable melting can be accumulated. As a result,improvement of productivity and reduction of electric power unitconsumption are attained.

[0269] (Embodiment 15)

[0270] An example of an arc-melting equipment shown in FIG. 30 will bedescribed here-below. The present example is an example wherein meltingis performed while oxygen is being blown in through two double tubetuyeres placed on a bottom of an melting chamber. The arc-meltingequipment has a melting chamber of a furnace diameter: 7.2 m; a height:4 m, a preheating chamber of a width: 3 m; a length: 5 m; a height: 7 mand a furnace capacity of 180 tons.

[0271] Firstly charged into the preheating chamber were 150 tons of ironscraps of a normal temperature and melting was begun using an upperelectrode of made graphite with a diameter of 30 inches using electricpower source of maximum 750 V, 130 KA. Immediately after an electriccurrent was turned on quick lime and fluorite were added and at the sametime oxygen was blown in at a rate of 4000 Nm³/hr through an oxygen blowlance. At the time when molten iron accumulated in the melting chamber,coke was blown, at a rate of 80 kg/min into slag to drive the slagforming operation and a top end of the upper electrode was buried in theslag which was forming. Voltage at this time was set to be 550 V. As theiron scraps in the preheating chamber descended following the melting,iron scraps were charged from the supply bucket into the preheatingchamber to maintain a level of the iron scraps in the preheating chamberat a certain height as the melting was continued.

[0272] During this time, oxygen was blown in through the double tubetuyere 40 Nm³/hr per one tuyere and 80 Nm³/hr per total tuyeres toprevent the cold iron source from hanging up and so that the cold ironsource dropped continuously into the molten iron. Propane gas was blownin through an outer tube of a double tube to cool the tuyere.

[0273] While iron scraps were continuously maintained in the meltingchamber and in the preheating chamber, the melting was promoted. When180 tons of the molten iron was produced in the melting chamber, 120tons for one charge was tapped into a ladle, leaving about 60 tons ofbehind in the melting chamber. At the tapping the molten iron was heatedby a heavy oil burner. Carbon concentration at the tapping was 0.1 wt %and temperature of the molten iron was 1550° C. After the tapping anelectric current was turned on again and at the same time injection ofoxygen and coke was commenced. When the molten iron amounted to 180 tonsagain tapping, 120 tons of the molten iron was repeated.

[0274] By maintaining the conditions that total oxygen blow amountthrough an oxygen blow lance and a bottom blow tuyere is at a rate of 33Nm³/t and that coke blow amount is 26 kg/t, the time from tapping totapping was 40 minutes on average and the electric power unitconsumption was reduced to 170 kWh/t, and melting could be completed.

[0275] In case that oxygen was not blown in through a tuyere, ironscraps which piled on a portion which had not yet melted were left notmelted in the vicinity of boundary of the molten iron and the cold ironsource. Furthermore, in spite of there being a pace below the ironscraps, the iron scraps did not fall down into the melting chamber. Thehanging-up was continued for a long time and that melting stagnatedabout once per 6 charge. According to the present invention, by blowingin oxygen, such stagnation of melting can be prevented.

[0276] As the results of investigating the relation between time fromtapping to tapping and its frequency with respect to the condition whereoxygen was blown in from a furnace bottom and the condition where oxygenwas not blown in, in the case that oxygen was not blown in as the sameas Example 1, supply of iron scraps to molten iron was delayed with theresult that the time from tapping to tapping was increased. But in thecase that oxygen was blown in tapping was accomplished about every 40minutes and extension of melting time did not occur.

[0277] Availability in Industry

[0278] As described above, since according to the present invention ironsource such as scraps is melted using an arc-melting equipment which hasa melting chamber and a preheat shaft directly connected to the upperportion of the melting chamber a device for carrying and supplying theiron source to the melting chamber is not required. Since the ironsource is being supplied so that the iron source is continuouslymaintained in the melting chamber and the preheat shaft, high efficiencycan be obtainable as below. Actually, in the present invention, the ironsource in the melting chamber is melted by an arc, and under conditionsthat the iron source is continuously maintained, in the melting chamberand in the preheat shaft, the molten iron is tapped, whereby the ironsource for next charge is also preheated. In addition since contactarea, the iron source and molten iron bath which is produced by meltingthe iron source can be made to be small, the molten iron can be superheated. This can solve a problem that temperature of the molten irontapped is too low. In addition, a part of or the whole of the bottomportion, which correspond to the preheat shaft of the melting chamber orcorrespond to the separating part, can have a slanted portion, from thebottom of the tapping portion (the deepest position) toward a directionwhich a furnace is tilted. The contact area with the iron source and themolten iron, can remarkably be small, in comparison with a case where abottom of the melting chamber does not have a slanted portion at abottom of the melting chamber. Therefore, the problem that temperatureof the molten iron is too low, can be avoided more effectively.

What is claimed is
 1. An arc-melting apparatus for melting a cold ironsource comprising: (a) a melting chamber which is used as a space formelting the cold iron source; (b) a preheating shaft directly connectedto an upper part of one side of the melting chamber, to preheat the coldiron source by introducing an exhaust gas generated in the meltingchamber; (c) an arc electrode for supplying heat for melting the coldiron source in the melting chamber; (d) a cold iron source supply devicefor supplying the cold iron source to the preheating shaft, so as tocontinuously maintain the cold iron source in the melting chamber and inthe preheating shaft; (e) a tapping portion having a tapping hole,projecting outwardly from the melting chamber; and (f) a tilting devicefor tilting the melting chamber toward the tapping portion.
 2. Theapparatus according to claim 1, wherein the tapping portion having thetapping hole is located in a different direction from a direction ofsupplying the cold iron source in the preheating shaft into the meltingchamber.
 3. The apparatus according to claim 2, wherein the tappingportion is arranged at an orthogonal direction to the direction of thesupplied cold iron source.
 4. The apparatus according to any one ofclaims 1 to 3, wherein a distance between a position where thepreheating shaft is placed adjacent to the melting chamber and aposition where the tapping portion is placed adjacent to the meltingchamber is predetermined to prevent the cold iron source from flowingout to the tapping portion, when the melting chamber is tilted.
 5. Theapparatus according to claim 4, wherein the distance between theposition where the preheating shaft is placed adjacent to the meltingchamber and the position where the tapping portion is placed adjacent tothe melting chamber, is longer than a horizontal distance that the coldiron source extends from the preheating shaft into the melting chamber.6. The apparatus according to claim 1, further comprising a travellingdevice for travelling the arc electrode, following the molten iron whichmoves in the melting chamber, when the melting chamber is tilted at atapping time.
 7. The apparatus according to claim 1, further comprisinganother arc electrode which is placed at the tapping portion.
 8. Theapparatus according to claim 1 , further comprising a device forsupplying an oxygen gas at a lower position of the preheating shaft. 9.The apparatus according to claim 1 , further comprising a fuel supplydevice for supplying a fuel, together with an oxygen gas to the coldiron source at a lower position of the preheating shaft.
 10. Theapparatus according to claim 1 , further comprising a carbonaceousmaterial supply device for supplying a carbonaceous material to themelting chamber and an oxygen gas supply device for supplying an oxygengas to the melting chamber.
 11. The apparatus according to claim 1 ,further comprising: a post-combustion chamber, for post-combusting aresidual of a combustible gas generated in the melting chamber which haspassed through the preheating shaft, by supplying an oxygen containinggas; a cooling portion which cools the exhaust gas discharged from thepost-combustion chamber; and a device for making a temperature of theexhaust gas discharged from the post-combustion chamber at least apredetermined temperature.
 12. The apparatus according to claim 1 ,further comprising an adsorbent supply device for supplying an adsorbentto the exhaust gas which has been quickly cooled at the cooling portion.13. The apparatus according to claims 1, further comprising; a devicefor combusting a part of a combustible gas generated from the meltingchamber, by arranging one or plural stages of a gas introducingentrances within a range from a surface of a molten iron bath in themelting chamber to a top position of the cold iron source at an upperpart of the preheating shaft and, by supplying an oxygen containing gasthrough the gas introducing entrances into a charge portion of the coldiron source.
 14. The apparatus according to claims 1, furthercomprising; a gas supply device for blowing an oxygen or an inert gasinto the molten iron in the vicinity of a boundary of the cold ironsource in the melting chamber and of the molten iron.
 15. A method forarc-melting a cold iron source comprising the steps of: (1) introducingan exhaust gas generated in a melting chamber into a preheating chamberto preheat the cold iron source; (2) melting the cold iron source in themelting chamber by an arc electrode, while continuously maintaining thecold iron source in the preheating shaft and in the melting chamber bycontinuously or intermittently supplying the cold iron source to thepreheating shaft; (3) tilting the melting chamber at the time when amolten iron has accumulated in the melting chamber; (4) heating themolten iron for a predetermined time by the arc electrode to rise atemperature of the molten iron; and (5) tapping the molten iron underconditions that the cold iron source is continuously maintained in thepreheating shaft and in the melting chamber.
 16. The method according toclaim 15, further comprising separating the molten iron and the coldiron source in the melting chamber completely, by tilting the meltingchamber.
 17. The method according to claim 15, further comprisingblowing an oxygen or the oxygen and fuel simultaneously onto the coldiron source at a lower position of the preheating shaft of the meltingchamber.
 18. The method according to claims 15 , further comprisingblowing oxygen and a carbonaceous material into the melting chamber. 19.The method according to claims 15, wherein the cold iron source issupplied at a rate whereby 40% or more of one charge remains in themelting chamber and in the preheating shaft during melting and tapping.20. The method according to claims 17, wherein the total amount of theoxygen blown into a lower part of the preheating shaft and the oxygenblown into the melting chamber is at least 25 Nm³/ton.
 21. The methodaccording to any one of claim 15, wherein the melting step comprises:melting the cold iron source in the melting chamber by supplying an archeat, a supplementary heat source and oxygen into the melting chamber;post-combusting a residual of combustible gas generated in the meltingchamber, which has passed through the preheating shaft, by supplying anoxygen containing gas into the melting chamber, without discharging theresidual of the combustible gas to the outside of the arc meltingstages; raising a temperature of the exhaust gas to a predeterminedtemperature or more; and cooling the exhaust gas continuously andquickly.
 22. The method according to claim 15 , wherein the melting stepcomprises; melting the cold iron source in the melting chamber bysupplying an arc heat , a supplementary heat source and an oxygen intothe melting chamber; arranging one or plural stages of gas introducingentrances within a range from the surface of the molten iron bath in themelting chamber to a top position of the cold iron source at an upperpart of the preheating shaft; and combusting a part or the whole of thecombustible gas generated from the melting chamber, by supplying anoxygen containing gas through the gas introducing entrances into thecharge portion of the cold iron source.
 23. The method according toclaim 21, further comprising supplying an adsorbent to the exhaust gaswhich has been quickly cooled at the cooling portion.
 24. The methodaccording to claim 21, wherein the exhaust gas after the post-combustionis at least 900° C.
 25. The method according to claims 15 , wherein themelting step comprises; melting the cold iron source in the meltingchamber, by supplying an arc heat, a supplementary heat source and anoxygen containing gas to the melting chamber; arranging one or pluralstages of the gas introducing entrances at a predetermined positions ina range from the surface of the molten iron bath in the melting chamberto an upper end position of the cold iron source at an upper part of thepreheating shaft; supplying a predetermined amount of an oxygencontaining gas through the gas introducing entrances to the chargeportion of the cold iron source to combust the combustible gas generatedfrom the melting chamber; raising the temperature of the exhaust gaswhich is generated by burning the combustible gas in the oxygencontaining gas at least a predetermined temperature in the vicinity ofthe outlet of the preheating shaft; and cooling the exhaust gas at thecooling portion which is connected to the upper part of the preheatingshaft.
 26. The method according to claim 25, wherein the melting stepcomprises supplying an adsorbent to the exhaust gas which has beenquickly cooled at the cooling portion.
 27. The method according to claim25, wherein the temperature of the exhaust gas in the vicinity of theoutlet of the preheating shaft is at least 900° C.
 28. The methodaccording to claims 22, wherein the total injected amount of the oxygencontaining gas is within a range in accordance to a following formula(A); 0.55Q≦Qin≦0.9Q  (A) in the formula (A), the supply oxygen amountQin is calculated from an oxygen concentration therein and a flow ratetherein , and an oxygen amount Q (Nm³/min) is the amount which isinjected into the melting chamber.
 29. The method according to claims15, wherein the melting step comprises: melting the cold iron source inthe melting chamber by supplying an arc heat and a supplementary heatsource to the melting chamber; melting the cold iron source in themelting chamber, by supplying an arc heat and a supplementary heatsource to the melting chamber; simultaneously introducing air into thismelting chamber and burning the incombustible gas in the melting chamberso that 0.3≦OD≦0.7 is realized where OD is CO₂/(CO₂+CO).